Method of Locating the Tip of a Central Venous Catheter

ABSTRACT

Methods of locating a tip of a central venous catheter (“CVC”) relative to the superior vena cava, sino-atrial node, right atrium, and/or right ventricle using electrocardiogram data. The CVC includes at least one electrode. In particular embodiments, the CVC includes two or three pairs of electrodes. Further, depending upon the embodiment implemented, one or more electrodes may be attached to the patient&#39;s skin. The voltage across the electrodes is used to generate a P wave. A reference deflection value is determined for the P wave detected when the tip is within the proximal superior vena cava. Then, the tip is advanced and a new deflection value determined. A ratio of the new and reference deflection values is used to determine a tip location. The ratio may be used to instruct a user to advance or withdraw the tip.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a division of U.S. patent application Ser. No.13/737,806, filed Jan. 9, 2013, which is a division of U.S. patentapplication Ser. No. 12/427,244, filed Apr. 21, 2009, now U.S. Pat. No.8,512,256, which is: 1) a continuation of International Application No.PCT/US2009/033116, filed Feb. 4, 2009, claiming priority under 35 U.S.C.§119(e) to U.S. Provisional Application No. 61/026,372, filed Feb. 5,2008; and 2) a continuation-in-part of U.S. patent application Ser. No.11/552,094, filed Oct. 23, 2006, now U.S. Pat. No. 7,794,407. Each ofthe aforementioned applications is incorporated by reference in itsentirety into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed generally to devices for and methodsof locating a catheter inside a body and more particularly to devicesfor and methods of locating the tip of a central venous catheter insidethe superior vena cava, right atrium, and/or right ventricle usinginformation obtained from an electrocardiogram.

2. Description of the Related Art

Central venous catheters (“CVC”) include any catheter designed toutilize the central veins (e.g., subclavian and superior vena cava) orright sided cardiac chambers for the delivery and/or withdrawal ofblood, blood products, therapeutic agents, and/or diagnostic agents.CVCs also include catheters inserted into the central veins or rightsided cardiac chambers for the acquisition of hemodynamic data. Standardcentral venous catheters for intravenous access, dialysis catheters,percutaneously introduced central catheters (“PICC” lines), and rightheart (“Swan-Ganz™”) catheters are examples of CVCs.

The standard of care for placing a CVC (other than right heart catheterswhich generally terminate in the pulmonary artery) dictates that the tipof the CVC lie just above and not inside the right atrium. In fact, in1989, the Food and Drug Administration issued a warning citing anincreased risk of perforation of the right atrium, clot formation, andarrhythmias among other potential complications resulting from the tipof the CVC being placed inside the right atrium.

While CVCs have been used for many years, determining the position ofthe tip of the CVC has always been problematic. Currently, a chest x-rayis used to determine the position of the tip of the CVC. Because CVC maybe a radiopaque and/or include radiopaque materials, the CVC is visibleon an x-ray. However, this method has several drawbacks. For example,obtaining a chest x-ray is labor intensive and expensive. In recentyears, CVCs, which were traditionally placed in a hospital in-patientsetting, are being placed in an outpatient setting more frequently. Inan outpatient setting, obtaining a chest x-ray to determine the positionof the tip of the CVC can be very cumbersome and may not be obtained ina timely manner. Therefore, using a chest x-ray to determine theposition of the tip of the CVC may introduce a considerable delay,prolonging the procedure. Generally, the operator will leave the patientto perform other duties while the x-ray is processed. If the tip isimproperly placed, the operator must return to the patient's bedside toreposition the CVC. To reposition the CVC, the operator must open thesterile dressing, cut the sutures, re-suture, and redress the wound, allof which potentially expose the patient to discomfort and infection.

Recently, navigational systems principally used to guide peripherallyplaced lines have become available. Based upon the detection of magneticfields between a stylet tip and a detector, these systems assume (anddepend upon) a relationship between surface landmarks and anatomiclocations. Unfortunately, these systems cannot be used to determine thelocation of the tip of a CVC with sufficient accuracy because therelationship between surface landmarks and anatomic locations is highlyvariable from one patient to another.

In addition to the need to know where the tip is during initialplacement, the CVC may migrate or otherwise move after the initialplacement and require re-positioning. Therefore, the operator mustmonitor or periodically reevaluate the location of the tip.

An electrocardiogram (“ECG”) measures electrical potential changesoccurring in the heart. Referring to FIGS. 1A-1C, the ECG measurementsmay be visualized or displayed as an ECG trace, which includes ECGwaveforms. As is appreciated by those of ordinary skill in the art, ECGwaveforms are divided into portions that include a QRS complex portionand a P wave portion in addition to other wave portions. The QRS complexcorresponds to the depolarization of the ventricular muscle. The P waveportion of the ECG waveforms represents atrial muscle depolarization:the first half is attributable to the right atrium and the second halfto the left atrium. Under normal circumstances, atrial muscledepolarization is initiated by a release of an excitatory signal fromthe sino-atrial (“SA”) node, a specialized strip of tissue located atthe juncture of the superior vena cava (“SVC”) and right atrium.

As is appreciated by those of ordinary skill in the art, an ECG may beobtained using different electrode configurations. For example, astandard configuration referred to as “Lead II” may used. In a bipolarLead II configuration, one of the electrodes (the cathode) is attachedto the left leg and the other electrode (the anode) is attached to theright shoulder. As is appreciated by those of ordinary skill in the art,using a different configuration could change the polarity and/or theshape of the P wave. Other standard bipolar configurations include abipolar Lead I configuration where the cathode is attached to the leftshoulder and the anode is attached to the right shoulder and a bipolarLead III configuration where the cathode is attached to the left leg andthe anode is attached to the right shoulder.

The waveforms depicted in FIGS. 1A-1C and 2B were obtained using theanode of a standardized bipolar ECG Lead II configuration attached tothe right shoulder and the tip of the CVC as the cathode. Whiletechnically this configuration is not a standard Lead II configuration,the trace produced by the electrodes 114A and 114B may be displayed on astandard ECG monitor using the monitor's circuitry to display the traceas a bipolar Lead II trace.

Techniques of using ECG waveforms to locate the tip of a CVC have beenavailable since the 1940's. Some of these prior art devices construct anintravascular ECG trace by placing an electrode near the tip of the CVCand using that electrode to measure the voltage near the tip of the CVCrelative to a surface electrode(s) and/or a second electrode spaced fromthe first.

These techniques have shown that both the magnitude and shape of the Pwave change depending upon the positioning or location of the electrodeattached to the tip of the CVC. Referring to FIGS. 1A and 1B, twoexemplary ECG traces are provided for illustrative purposes.

FIG. 1A is an ECG trace made when the electrode attached to the tip ofthe CVC is in the proximal SVC. This tip location corresponds toposition “1” depicted in FIG. 2A. The portion of the ECG tracecorresponding to an exemplary P wave produced when the electrodeattached to the tip is located in position “1” is labeled “P1.”

FIG. 1B is an ECG trace made when the electrode attached to the tip ofthe CVC is approaching the SA node and stops at a location adjacent tothe SA node. These tip locations correspond to moving the tip from aposition “2” to position “3” depicted in FIG. 2A. The portion of the ECGtrace corresponding to an exemplary P wave produced when the electrodeattached to the tip is approaching the SA node is labeled “P2” and theportion of the ECG trace corresponding to an exemplary P wave producedwhen the electrode attached to the tip is located adjacent to the SAnode is labeled “P3.”

Normally as the electrode attached to the tip of the CVC moves from theproximal SVC (position “1”) toward the SA node (position “3”), themaximum value of the absolute value of the voltage of the P waveincreases dramatically. When the electrode attached to the tip of theCVC is adjacent to the SA node (position “3”), the voltage of the P wave(please see “P3” of FIG. 1B) reaches a maximum value that is more thantwice the value experienced in the proximal SVC and may be as large aseight times the voltage in the proximal SVC. When this occurs, the tipof the CVC is considered to have entered into the right atrium. Becausethe magnitude of the P wave more than doubles when the electrodeattached to the tip of the CVC is adjacent to the SA node, thisinformation may be used to place the tip of the CVC within a fewcentimeters (e.g., about 1 cm to about 2 cm) proximal to the SA node.Additionally, as the electrode attached to the tip of the CVC moves fromthe proximal SVC toward the right atrium, the shape of the P wavechanges from a “u” shape (FIG. 1A) to a spike-like shape (FIG. 1B).

Referring to FIG. 2B, another exemplary illustration of the P waveportion of the ECG trace produced when the electrode attached to the tipof the CVC is located at positions 1-5 depicted in FIG. 2A is provided.The P wave portions of the ECG traces of FIG. 2B are labeled with theletter “P” and occur between the vertical dashed lines. Each of theexemplary traces is numbered to correspond to positions “1” through “5.”Therefore, the ECG trace “1” was produced when the electrode attached tothe tip was located in the proximal SVC. The trace “2” was produced whenthe electrode attached to the tip was in position “2” (distal SVC). Thetrace “3” was produced when the electrode attached to the tip wasadjacent to the SA node.

As the electrode attached to the tip of the CVC is advanced further intothe right atrium, the polarity of the P wave “P” changes frompredominantly negative near the top of the right atrium (position “3”)to isoelectric (i.e., half has a positive polarity and half has anegative polarity) near the middle of the right atrium (position “4”) toalmost entirely positive at the bottom of the right atrium (position“5”). These changes in the P wave “P” are illustrated in traces “3”through “5.”

FIG. 1C is an ECG trace made when the electrode attached to the tip ofthe CVC is in the right ventricle. The portion of the ECG tracecorresponding to an exemplary P wave produced when the electrodeattached to the tip is labeled “P6.” When the electrode attached to thetip of the CVC is advanced into the right ventricle, the maximummagnitude of the absolute value of the P wave “P6” approximates themaximum magnitude of the absolute value of the P wave “P1” when theelectrode attached to the tip of the CVC was inside the proximal SVCabove the SA node (i.e., located at position “1”). However, the polarityof the first half of P wave “P6,” which corresponds to the right atrium,is opposite.

The first technique developed for viewing the ECG waveform during theinsertion of a CVC used a column of saline disposed within a hollow tubeor lumen longitudinally traversing the CVC. The column of salineprovides a conductive medium. Saline was inserted into the lumen by asaline filled syringe with a metal needle. The needle of the syringeremained within the entrance to the lumen or port in contact with thecolumn of saline after the lumen was filled. One end of a double-sidedalligator clip was attached to the needle and the other end was attachedto an ECG lead, which in turn was attached to an ECG monitor. By usingthe saline solution filled CVC as a unipolar electrode and a secondvirtual electrode generated by ECG software from three surfaceelectrodes, an intravascular ECG was obtained. The operator would adjustthe position of the tip of the CVC based on the magnitude and shape ofthe P wave displayed by the ECG monitor.

Subsequently, this technique was modified by substituting anArrow-Johans adapter for the metal needle. The Arrow-Johans adapter is astandard tubing connector with an embedded conductive ECG eyelet. TheArrow-Johans adapter may be placed in line with any conventional CVC. Ina closed system, the tubing and CVC may be filled with saline, i.e., aconductive medium, and the CVC used as a unipolar electrode inconjunction with surface electrodes and a standard ECG monitor. The ECGeyelet is placed in contact with the saline in the lumen of the CVC. Oneend of the ECG lead is attached to the ECG eyelet and the other end tothe ECG monitor for displaying the intravascular ECG waveforms. Becausethe system must be closed to prevent the saline from leaking out, thissystem works best after the guide wire used to thread the CVC forwardhas been withdrawn, i.e., after placement has been completed. Therefore,although the catheter may be withdrawn after initial placement, it maynot be advanced into proper position.

B. Braun introduced its Certofix catheter to be used in conjunction withits CERTODYN adapter. In this system, a patch lead with two ends has analligator clip connected to one end. The alligator clip is clipped tothe CVC guide wire. The other end of the patch lead includes a connectorthat is plugged into the CERTODYN adapter. The ECG may be obtainedduring placement and the catheter may be advanced or withdrawn asdesired. However, the CERTODYN adapter has many moving parts and is notsterile, making the procedure cumbersome to perform and the operativefield more congested. Additionally, the sterile field may becomecontaminated by the non-sterile equipment.

The Alphacard, manufactured by B. Braun, merges the Arrow-Johans adapterand the CERTODYN adapter. The Alphacard consists of a saline filledsyringe (used to flush the CVC with saline) and a connector to theCERTODYN. The Alphacard is used to obtain a ‘snapshot’ of the ECG tracefrom the saline column. If an atrial spike is seen in the ECG trace, theCVC is withdrawn.

With respect to all of these prior art methods of using an ECG trace toplace the tip of the CVC, some degree of expertise is required tointerpret the P waves measured because the user must advance the guidewire slowly and watch for changes in the P wave. If the catheter isinserted too far too quickly and the changes to the P wave go unnoticed(i.e., the operator fails to notice the increase or spike in the voltageexperienced when the electrode attached to the tip is in the rightatrium), the operator may mistakenly believe the tip is in the SVC when,in fact, the tip is in the right ventricle. If this occurs, advancingthe tip may injure the patient.

U.S. Pat. Nos. 5,078,678 and 5,121,750 both issued to Katims teach amethod of using the P wave portion of an ECG trace to guide placement ofthe tip of the CVC. The CVC includes two empty lumens into which atransmission line is fed or an electrolyte is added. Each of the lumenshas a distal exit aperture located near the tip of the CVC. The two exitapertures are spaced from one another. In this manner, two spaced apartelectrodes or a single anode/cathode pair are constructed near the tipof the CVC. The voltage or potential of one of the electrodes relativeto the other varies depending upon the placement of the electrodes. Thevoltage of the electrodes is conducted to a catheter monitoring system.The catheter monitoring system detects increases and decreases in thevoltage of the P wave. The voltage increases as the electrodes approachthe SA node and decrease as the electrodes move away from the SA node.Based on whether the voltage is increasing or decreasing, the operatoris instructed by messages on a screen to advance or withdraw the CVC.

While Katims teaches a method of locating the tip of a CVC relative tothe SA node, Katims relies on advancing or withdrawing the CVC andobserving the changes of the P wave. Katims does not disclose a methodof determining the location of the tip of the CVC based on a singlestationary position. Unless the entire insertion procedure is monitoredcarefully, the method cannot determine the position of the tip of theCVC. Further, the Katims method may be unsuitable for determining thelocation of a previously positioned stationary tip.

Other devices such as Bard's Zucker, Myler, Gorlin, and CVP/Pacing LumenElectrode Catheters are designed primarily to pace. These devicesinclude a pair of electrodes at their tip that are permanently installedand designed to contact the endocardial lining. These devices include alumen, which may be used to deliver and/or withdraw medications orfluids as well as for pressure monitoring. These leads are not designedfor tip location and do not include multi-lumen capability.

A method of obtaining an intravascular ECG for the purposes of placing atemporary pacing wire was described in U.S. Pat. No. 5,666,958 issued toRothenberg et al. Rothenberg et al. discloses a bipolar pacing wirehaving a distal electrode. The distal electrode serves as a unipolarelectrode when the pacing wire is inserted into the chambers of theheart. The pacing wire is connected to a bedside monitor through aspecialized connector for the purposes of displaying the ECG waveformsdetected by the distal electrode.

Given the volume of CVCs placed yearly and the increasing demandparticularly for PICC lines (devices that permit the delivery ofintravenous therapeutic agents in the outpatient setting, avoiding theneed for hospitalization) a great need exists for methods and devicesrelated to locating the tip of a CVC. Particularly, devices and methodsare needed that are capable of determining the location of the tipbefore the operator leaves the bedside of the patient. Further, a methodof determining the location (SVC, right atrium, or right ventricle) ofthe tip from a single data point rather than from a series of datapoints collected as the catheter is moved may be advantageous. Such asystem may be helpful during initial placement and/or repositioning. Aneed also exists for a device for or a method of interpreting the ECGwaveforms that does not require specialized expertise. Methods anddevices that avoid the need for hospital and x-ray facilities are alsodesirable. A need also exists for devices and methods related todetermining the position of the tip of the CVC that are less expensive,expose patients to fewer risks, and/or are less cumbersome than thex-ray method currently in use.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1A is an exemplary ECG trace obtained from an electrode placedinside the proximal SVC.

FIG. 1B is an exemplary ECG trace obtained from an electrode approachingthe sino-atrial node and stopping adjacent thereto.

FIG. 1C is an exemplary ECG trace obtained from an electrode placedinside the right ventricle.

FIG. 2A is an illustration of a partial cross-section of the heartproviding five exemplary tip locations 1, 2, 3, 4, and 5.

FIG. 2B is a series of exemplary P wave traces 1, 2, 3, 4, and 5obtained from an electrode placed in each of the exemplary tip locations1, 2, 3, 4, and 5 depicted in FIG. 2A, respectively.

FIG. 3A is a signal analysis system configured to determine the positionof the tip of a CVC using a single pair of electrodes.

FIG. 3B is an embodiment of a CVC including three pairs of electrodes.

FIG. 4 is a block diagram illustrating a method of using a single pairof electrodes to locate the tip of the CVC within the SVC.

FIG. 5 is a block diagram illustrating a method of using a single pairof electrodes to determine the tip of the CVC is located within theright ventricle.

FIG. 6 is a block diagram illustrating a method of using a single pairof electrodes to determine the location of the tip of the CVC within theright atrium.

FIG. 7 is an embodiment of a signal analysis system for use with the CVCof FIG. 3B.

FIG. 8 is a block diagram illustrating the components of the signalanalysis system of FIG. 7.

FIG. 9 is block diagram illustrating the components of a monitor of thesignal analysis system of FIG. 3A.

FIG. 10 is a block diagram illustrating a method of using at least twopairs of electrodes to locate the tip of the CVC relative to the SVC,right atrium, and right ventricle.

FIGS. 11A-11B are a block diagram illustrating an alternate method ofusing a single pair of electrodes to locate the tip of the CVC relativeto the SA node.

DETAILED DESCRIPTION OF THE INVENTION Central Venous Catheter 100

Aspects of the present invention are directed toward a device forlocating the tip of a central venous catheter (“CVC”) and a method ofdetermining the location of the tip of a CVC. The embodiments depictedin FIGS. 3A and 3B, include a CVC 100 constructed using any manner knownin the art from a flexible nonconductive material, such as polyurethaneor other suitable polymer material. It may also be desirable to use aradiopaque material to construct the CVC 100. As is appreciated by thoseof ordinary skill in the art, the material used to construct the CVC 100may include materials and/or coatings that provide improvedanti-thrombotic or anti-bacterial properties. The CVC 100 has a body 130configured to be received within a central vein. The body 130 mayinclude a distal end 110 having a tapered tip 112 and a proximal end 120spaced longitudinally along the body 130 from the distal end 110.

Referring to FIG. 3A, the body 130 may include one or more lumens 132that traverse the length of the body and may have one or more openings134 at or spaced from the tip 112 and an open end portion 122 configuredto permit access into the lumen 132. When the tip 112 of the CVC 100 isreceived within a central vein, the open end portion 122 may remainoutside the central vein allowing materials (e.g., saline, mediations,etc.) to be inserted into the lumen 132 while the tip 112 is inside thecentral vein or another anatomical structure. The opening 134 permitsthe passage of materials between the lumen 132 and the environmentoutside the CVC 100. If one or more materials are inserted into thelumen 132 via the open end portion 122, those materials may exit thelumen 132 via the opening 134. If materials enter the lumen 132 via theopening 134, those materials may exit the lumen 132 via the open endportion 122.

The open end portion 122 is configured be coupled to a connector 124through which materials may be introduced into or exit from the open endportion 122 of the lumen 132. The connector 124 may include any suitableconnector known in the art including a Tuohy-Borst adapter, stop cock,and the like. In the embodiment depicted in FIG. 3A, the connector 124is a Tuohy-Borst adapter, which includes a side port 125 through whichmaterials (e.g., saline) may be introduced into the open end portion 122of the lumen 132. The side port 125 may be used to flush the lumen 132with normal saline or another material. The connector 124 is configuredto maintain materials within the lumen 132 and to prevent thosematerials from leaking out of the CVC 100 through the open end portion122.

The lumens 132 may be used as conduits for the passage of materials suchas medications and/or other fluids to and from the environment outsidethe CVC 100. For example, the lumen 132 may be used to aspirate bloodinto the CVC 100 and/or provide a conduit through which pressure datamay be collected and used to construct pressure waveforms. Theenvironment outside the CVC 100 may include the inside of the SVC, rightatrium, and/or right ventricle. The CVC 100 is provided for illustrativepurposes and those of ordinary skill in the art appreciate thatalternate embodiments of CVC 100 including embodiments with additionallumens, a flow directed balloon tip, thermistors, thermodilution ports,pacing wire ports, embedded pacing electrodes, and the like are withinthe scope of the present invention.

Deflection Value

The deflection of an ECG trace, (i.e., its vertical height relative tothe baseline) may be used to compare two or more P waves. Because a Pwave constitutes a voltage change over time, the deflection of the Pwave is not constant. In particular embodiments, the P wave isrepresented by an array or series of discrete numerical values.

The deflection value may be calculated in several ways. For example, themaximum or peak deflection may be used. Alternatively, the deflectionvalue may be calculated as the difference between the maximum deflectionand the minimum deflection. The deflection value may also be calculatedas the sum of the absolute value of the maximum and minimum deflections.If the P wave has two peaks, which may occur when the tip 112 is locatedwithin the right atrium and the P wave is biphasic (see position 4 ofFIGS. 2A and 2B), the deflection value may be calculated by totaling theabsolute value of the two peaks. When this method is used, thedeflection value of the P wave measured at positions 3-5 may all beapproximately equal. Further, if discrete data is being used, thedeflection value may also be calculated as a total of the discretedeflection quantities. If continuous data is being used, the deflectionvalue may also be calculated as the integral under the P wave. Further,the deflection value may also be calculated as the average P wavedeflection. Because the polarity of portions of the P wave changedepending upon the location of the tip 112, it may be beneficial to usethe absolute value of the deflection of the P wave to calculate thedeflection value.

For the purposes of this application, the term “deflection value” willbe used hereafter to describe the metric used to compare two or more Pwaves, which depending upon the implementation details may be detectedby one or more pairs of electrodes. It is appreciated by those ofordinary skill in the art that the deflection value may be determined innumerous ways including those listed above and others not listed and theinvention is not limited by the method and manner of determining thedeflection value of the P wave.

In the embodiments discussed below, unless otherwise indicated, thedeflection value is calculated as the sum of the absolute value of themaximum and minimum deflections when the maximum and minimum deflectionshave opposite polarities. The deflection value is calculated as thelarger of the absolute value of the maximum and minimum deflections whenthe maximum and minimum deflections have the same polarity. In otherwords, the vertical height of the P wave is used.

Embodiments Using a Single Pair of Electrodes

Referring to FIG. 3A, an embodiment of a system 121 using a single pairof electrodes 114 to determine the position of the tip 112 of the CVC100 will be described. An electrolytic material or solution, such assaline, may be disposed inside the lumen 132. The electrolytic materialinside the lumen 132 forms a continuous conductor or column ofelectrolytic material that may be used to conduct an electrical signalfrom the opening 134 in the tip 112, and up the continuous column. Inother words, the opening 134 exposes the electrolytic material insidethe lumen 132 to electrical activity occurring in the environmentoutside the tip 112. A first electrode 114A of the pair of electrodes114 is placed in electrical communication with the continuous columninside the lumen 132. The first electrode 114A may be coupled by a wire123 to a monitor 127.

A second or surface electrode 114B is placed in contact with the skin ofa patient. By way of a non-limiting example, the surface electrode 114Bmay be affixed to the skin of the patient's chest using any method knownin the art. The surface electrode 114B is coupled to the monitor 127 bya wire 129. The voltage at or near the opening 134 in the tip 112 may bemeasured using the pair of electrodes 114.

The voltages detected by the pair of electrodes 114 may be used tocreate an ECG trace of the electrical activity observed at or near thetip 112 of the CVC 100. Because the voltage across each of the pair ofelectrodes 114 may vary with time, the voltage across wires 123 and 129may constitute a time-varying signal that can be analyzed using standardsignal processing methods well known in the art. In a typical patient,the maximum voltage across the pair of electrodes 114 may range fromabout 0.2 mV to about 3 mV. The signal detected by the pair ofelectrodes 114 may be amplified and/or filtered to improve the signalquality.

In the embodiment depicted in FIG. 3A, the first electrode 114A iscoupled to the connector 124. Alternatively, the first electrode 114Amay be located inside at least a portion of the lumen 132. By way ofanother example, the first electrode 114A is coupled to the side port125 through which the electrolytic material (e.g., saline) may beintroduced into the open end portion 122 of the lumen 132. As isapparent to those of ordinary skill in the art, the first electrode 114Amay be located anywhere that would place it in electrical continuity orcommunication with the electrolytic material (e.g., saline) exiting thetip 112 via the opening 134 or otherwise communicating electrically withthe environment outside the opening 134 of the tip 112. By way ofanother example, the first electrode 114A may be incorporated into aguide wire (not shown), stylet, and the like that extends from, or nearthe tip 112 up the body 130 of the CVC 100 and is electrically coupledby the wire 123 to the monitor 127. The monitor 127 is described indetail below.

Method of Using a Single Electrode Pair To Determine the Position of theTip of the CVC

Referring to FIG. 4, a method 140 of determining the location of the tip112 using the pair of electrodes 114 will now be described. In block141, the CVC 100 is inserted into the SVC. The CVC 100 may gain venousaccess to the SVC by any method known in the art including inserting theCVC 100 in a standard sterile fashion through the subclavian, one of thejugular veins, or a peripheral vein and directing the tip 112 of the CVC100 through that vein toward the proximal SVC.

Next, in block 142, a reference deflection value is recorded in astorage location. The reference deflection value is the deflection valueobtained from the pair of electrodes 114 when the tip 112 is located inthe venous system proximal to or in the proximal SVC.

Then, in block 143, the tip 112 is advanced. As the tip 112 is advanced,a ratio of the deflection value of the currently observed P wave to thereference deflection value is calculated. Inside the SVC, as the tip 112approaches the mid SVC, the deflection value of the P wave may increaseby two to four times the reference deflection value. Further, as the tip112 approaches the distal SVC, the deflection value of the P wave mayincrease by four to six times the reference deflection value. In thedistal SVC near the SA node, the deflection value of the P wave mayincrease by six to eight times the reference deflection value.

In decision block 144, whether the ratio is less than or equal to afirst predefined threshold value is determined. The first predefinedthreshold value should be large enough to ensure the tip 112 has leftthe proximal SVC and entered the mid SVC. Further, the first predefinedthreshold value should be small enough to prevent placement of the tip112 in the distal SVC. Thus, the first predefined threshold value may bewithin a range of about 1.6 to about 3.9. By way of a non-limitingexample, the first predefined threshold value may be about 2.0. If theratio is less than or equal to the first predefined threshold value, inblock 143, the tip 112 may be advanced and the ratio recalculated. Ratiovalues less than or equal to the first predefined threshold valueindicate the tip 112 is in the proximal or mid SVC and has not yetreached either the distal SVC, caval-atrial junction adjacent to the SAnode or the upper right atrium.

If decision block 144 determines the ratio is not less than or equal tothe first predefined threshold value, the method 140 advances todecision block 145. In decision block 145, whether the ratio is lessthan or equal to a second predefined threshold value is determined. Thesecond predefined threshold value should be large enough to ensure thetip 112 is in the distal SVC and small enough to avoid entry of the tip112 into the right atrium. By way of a non-limiting example, the secondpredefined threshold value may within a range of about 4.0 to about 8.0.By way of a non-limiting example, the second predefined threshold valuemay be about 8.0. In other words, the block 144 determines whether theratio is between the first and second threshold values or within a rangedefined between the first and second threshold values (e.g., about 2.0to about 8.0). Nevertheless, ratio values within the range definedbetween the first and second threshold values may indicate the tip 112is approaching or has reached the SA node, or the tip is located withinthe right atrium. In other words, any ratio value above the secondpredefined threshold value may indicate the tip 112 is located in thedistal SVC or the upper atrium. If the ratio is within the range definedbetween the first and second threshold values, the decision in decisionblock 145 is “YES” and the method 140 ends.

If the ratio is greater than the second threshold value, the decision indecision block 145 is “NO,” and the method 140 advances to block 147.When the ratio is greater than the second threshold value, the tip 112is in or near the right atrium and in block 147, the user or operator isadvised to withdraw the tip 112. By way of a non-limiting example, theuser or operator may be advised to withdraw the tip 112 about 0.5 cm toabout 1 cm. Then, in block 147, advancement of the tip 112 is terminatedand the tip 112 withdrawn. By way of a non-limiting example, the user oroperator may withdraw the tip 112 about 0.5 cm to about 1 cm. In block147, as the tip 112 is withdrawn, the ratio of the deflection value ofthe currently observed P wave to the reference deflection value isrecalculated.

Then, the method 140 returns to decision block 144.

In particular embodiments, if at any time during the performance ofmethod 140, the ratio is equal to the second predefined threshold value,the tip 112 is maintained in its current position without additionaladvancement or withdrawal and the method 140 ends. When the method 140ends, the ratio is between the first and second threshold values and thetip 112 is located in the mid SVC or distal SVC.

The following table, Table 1, summarizes the relationship between thelocation of the tip 112 of the CVC 100 and the ratio of the deflectionvalue of the currently observed P wave to the reference deflectionvalue:

TABLE 1 Location of the tip 112 Very Distal Proximal Mid Distal SVC orRight SVC SVC SVC Atrium Ratio: ratio of the ≦1.5 1.6-4.04.1-5.5 >5.5-8.0 deflection value of the currently observed P wave tothe reference deflection value

While Table 1 provides exemplary ranges and/or threshold values for useas a general guideline, those of ordinary skill in the art appreciatethat these values may benefit from adjustment as additional anatomic orelectrophysiologic data is acquired and such modified values are withinthe scope of the present invention.

As is apparent to those of ordinary skill, the pair of electrodes 114may be used to detect the instantaneous location of the tip 112.Therefore, if the tip 112 migrates into the atrium, this movement may bedetected immediately by calculating a ratio of the deflection value ofthe currently observed P wave to the recorded reference deflection valueand comparing the ratio to the first and second threshold values. Thiscalculation may be performed periodically or at random intervals. If thetip 112 migrates into the atrium, a medical professional may be alertedvia a signal, such as an alarm, and the like, to reposition the tip 112.

Referring to FIG. 5, a method 450 may be used to determine the tip 112is located within the ventricle. In first block 452, the tip 112 islocated in the atrium. Then, in block 454, a reference atrium deflectionvalue is recorded. The reference atrium deflection value is thedeflection value obtained from the pair of electrodes 114 when the tip112 is located in the atrium. Then, in block 456, a ratio of thedeflection value of the current P wave detected by the pair ofelectrodes 114 to the reference atrium deflection value is determined.In decision block 457, whether the ratio is greater than a thirdpredefined threshold value is determined. The third predefined thresholdvalue may be about 0.5. If the decision is “YES,” the ratio is greaterthan the third predefined threshold value, and in block 458, the tip 112is determined to be in the right atrium. Then, the method 450 ends. Ifthe decision in decision block 457 is “NO,” the ratio is less than orequal to the third predefined threshold value, and in block 459, the tip112 is determined to be in the right ventricle. Then, the method 450ends.

Within at least a portion of the range defined between the first andsecond threshold values (e.g., about 2.0 to about 8.0), the P wavevoltage measured using prior art techniques, such as those disclosed byU.S. Pat. Nos. 5,078,678 and 5,121,750 (both issued to Katims), hasgenerally not yet reached its maximum value. Therefore, the presentmethod indicates the tip 112 should be withdrawn before those techniqueswould signal withdrawal. For example, typically the P wave voltagewithin the proximal SVC is about 0.2 to about 0.3 mV. Near the SA node,the P wave voltage may increase about 8 fold (e.g., about 1.6 mV toabout 2.4 mV. In other words, the ratio is about 8 near the SA node,which is the location of the maximum P wave voltage used in the priorart. However, prior art techniques advise to advance the tip until itcan be clearly seen that the maximum P voltage has been reached.Therefore, the prior art techniques allow the tip 112 to advance furtherinto the right atrium than the present technique before identifying theadvancement should be halted and the tip withdrawn back into the SVC.Because the present technique halts the advancement of the tip 112earlier (e.g., when the P wave voltage increases above the secondpredefined threshold value of about 8.0, which corresponds to about 1.6mV to about 2.4 mV) than prior art techniques, the present teachings mayavoid many of the risks associated with advancing the tip into the rightatrium.

Further, the prior art teaches using a threshold percentage decrease todetermine the tip 112 is in the correct location. However, using athreshold percentage decrease may be ineffective at locating the tip 112within the SVC because the percentage decrease may vary from patient topatient. In other words, depending upon the anatomical structures of thepatient, the tip 112 may have to be withdrawn until the percentagedecreases differing amounts. On the other hand, if the tip 112 iswithdrawn until the ratio is between about 2.0 and about 8.0 (e.g., thecurrent P wave voltage is about 0.4 mV to about 2.4 mV), the tip will belocated in the mid SVC or in some cases, the distal SVC. Therefore, thepresent technique more accurately positions the tip 112 than prior arttechniques.

In addition to halting the advancement of the tip 112 when the ratio ofthe deflection value of the currently observed P wave to the referencedeflection value has exceeded either of the first and second predefinedthreshold values, advancement of the tip 112 could also be halted whenthe deflection value of the currently observed P wave is approximatelyequivalent to the voltage (or deflection value) of the QRS complex.

As discussed above, when observed using a standard bipolar Lead IItrace, the P wave voltage is almost entirely negative at the top of theright atrium (see trace 3 of FIG. 2B), biphasic in the mid right atrium(see trace 4 of FIG. 2B), and positive at the bottom of the right atrium(see trace 5 of FIG. 2B). A positive/total deflection ratio may becalculated and used to determine when advancement of the tip 112 shouldbe halted. The positive/total deflection ratio is a ratio of thegreatest positive deflection value (of an initial positive or upwardlydeflecting portion that precedes a downwardly deflecting portion) to thetotal deflection value of the currently observed P wave. When thepositive/total deflection ratio is greater than a predetermined fraction(e.g., one quarter, one eighth, etc.) advancement of the tip 112 shouldbe halted. For example, the traces 3-5 illustrated in FIG. 2B each havean initial upwardly deflecting portion. However, in both cases, thegreatest positive deflection value of the initial upwardly deflectingportion of the P wave is clearly greater than one quarter of the totaldeflection value of the currently observed P wave. As explained above,in these traces, the tip 112 is located in the right atrium. Thus, ifthe greatest positive deflection value is greater than the predeterminedfraction of the total deflection value of the currently observed P wave,the tip 112 is in the right atrium and should be withdrawn.

Alternate Method of Using a Single Electrode Pair to Determine thePosition of the Tip of the CVC

FIGS. 11A and 11B provide a block diagram of an alternate method 600 ofadvancing and locating the tip 112 of the CVC 100. A physicalcathode-anode electrode pair is used in a standard bipolar lead setup. Abipolar lead setup means two physical leads are used (rather than onevirtual lead and one physical lead, which are referred to as a unipolarlead setup).

For illustrative purposes, the method 600 is described using the firstelectrode 114A (see FIG. 3A) functions as a cathode at the tip 112 andthe second electrode 114B (see FIG. 3A) functions as an anode attachedto the patient's skin near his/her right shoulder. The continuousconductor or column inside the lumen 132, which is in electricalcommunication with both the first electrode 114A and the electricalactivity occurring in the environment outside the tip 112 functions as a“wandering electrode,” which is the positive cathode. The secondelectrode 114B serves as the negative anode electrode. While technicallythis configuration is not a standard Lead II configuration, the traceproduced by the electrodes 114A and 114B may be displayed on a standardECG monitor using the monitor's circuitry to display the trace as abipolar Lead II trace. Thus, an ECG trace is generated for the wanderingelectrode relative to the electrode “RA,” which is displayed as a LeadII trace. However, as is apparent to those of ordinary skill in the art,through application of ordinary skill in the art to the presentteachings other ECG Lead traces could be used and are within the scopeof the present disclosure.

As is apparent to those of ordinary skill in the art, in a standardunipolar lead setup, three surface electrodes (not shown) are attachedto a patient's skin: an electrode “RA” is attached to the patient'sright arm (or shoulder), an electrode “LA” is attached to the patient'sleft arm (or shoulder), and an electrode “LL” is attached to thepatient's left leg. A virtual electrode may be created using ECGsoftware, which calculates the virtual electrode as the electricalcenter of an Einthoven's triangle created by the electrodes “RA,” “LA,”and “LL” used in the Lead I, Lead II, and Lead III configurations. Thecontinuous conductor or column inside the lumen 132, which is inelectrical communication with both the first electrode 114A and theelectrical activity occurring in the environment outside the tip 112functions as a “wandering electrode.” The wandering electrode is thepositive cathode, and the virtual electrode is the negative anodeelectrode. Thus, an ECG trace is derived for the wandering electroderelative to the virtual electrode. In addition to Leads I, II, and III(of the bipolar configurations), some ECG monitors display unipolar leadconfigurations, e.g., aVR, aVL, aVF derived from a composite of theelectrodes “RA,” “LA” and “LL,” or a chest electrode, variably called a“V,” “MCL,” or “Chest” lead (hereafter referred to as the “V” lead).Some ECG monitors display this ECG trace as a unipolar “V” lead traceand some users particularly like to use the unipolar “V” lead trace toguide the tip 112 of the CVC 100. However, most users use the bipolarLead II trace generated for the wandering electrode relative to theelectrode “RA” (i.e., the ECG Lead II configuration discussed above). Asis apparent to those of ordinary skill in the art, with respect to themethod 600, any number of bipolar or unipolar lead configurations may beused with acceptable results. Further, either the unipolar “V” leadtrace or the bipolar Lead II trace (among others) may be used to performthe method 140.

In method 600, the deflection values measured include only the negativepolarity or downwardly extending portion of the P-wave. The upwardlyextending positive polarity portion is not included in the measurementof the deflection values. Thus, the deflection value is calculated asthe absolute value of the minimum deflection.

In first block 610, the CVC 100 is introduced into the venous system andadvanced to an initial location estimated to place the tip 112 of theCVC 100 at or proximal to the proximal SVC. In next block 620, adeflection value of the P wave observed at the initial location ismeasured and stored as a reference deflection value.

Then, in block 630, the CVC 100 is advanced from the initial location toa second location. By way of a non-limiting example, the CVC 100 may beadvanced from the initial location about 0.5 cm to about 1.0 cm in block630. At the second location, a new deflection value is measured using ofthe P wave observed at the second location. A deflection ratio of thenew deflection value to the reference deflection value is thencalculated. As the method 600 is performed, a maximum deflection ratioobserved is stored. Thus, in block 630, the maximum deflection valueobserved is equal to the deflection ratio observed at the secondlocation.

In block 640, the CVC 100 is advanced from the second location by anincremental distance. By way of a non-limiting example, the incrementaldistance may be within a range of about 0.5 cm to about 1.0 cm. However,a smaller sized incremental distance may be used and is within the scopeof the present teachings.

After the CVC 100 has been advanced by the incremental distance, inblock 650, a current deflection value of the P wave observed at the newlocation is measured and a current deflection ratio of the currentdeflection value to the reference deflection value is calculated. If thecurrent deflection ratio is greater than the maximum deflection ratio,the maximum deflection ratio is set equal to the current deflectionratio. Before the CVC 100 was advanced, the CVC was located a previouslocation. The deflection value measured at the previous location is aprevious deflection value and the deflection ratio of the previousdeflection value to the reference deflection value is a previousdeflection ratio.

Then, in decision block 660, the current deflection ratio is compared tothe previous deflection ratio. The decision in decision block 660 is“YES” when the current deflection ratio is less than the previousdeflection ratio. Otherwise, the decision in decision block 660 is “NO.”

When the decision in decision block 660 is “YES,” in block 665, the CVC100 is withdrawn from the current location to a new location. By way ofa non-limiting example, in block 665, the CVC 100 may be withdrawn about0.5 cm to about 1.0 cm. Then, a new deflection value of the P waveobserved at the new location is measured and a new deflection ratio ofthe new deflection value to the reference deflection value iscalculated. If the new deflection ratio is greater than the maximumdeflection ratio, the maximum deflection ratio is set equal to the newdeflection ratio. At this point, the location of the CVC 100 beforewithdrawal is a previous location and the deflection ratio calculated atthe previous location is a previous deflection ratio. The location ofthe CVC 100 after withdrawal is a current location and the deflectionratio calculated at the current location is a current deflection ratio.By way of a non-limiting example, the CVC 100 may be withdrawn about 1cm. Then, the method 600 advances to decision block 670.

In decision block 670 whether the CVC 100 has been withdrawn far enoughis determined. In decision block 670, a positive/total deflection ratioof the greatest positive deflection value (of an initial positive orupwardly deflecting portion which precedes a downwardly deflectingportion) to the total deflection value of the currently observed P waveis calculated. The decision in decision block 670 is “YES” when thepositive/total deflection ratio is less than a predetermined fraction(e.g., one quarter, one eighth, etc.). Otherwise, the decision indecision block 670 is “NO.”

Alternatively, in decision block 670, a negative/total deflection ratioof the smallest negative deflection value (of a negative polarity ordownwardly deflecting portion of the currently observed P wave whichfollows an upwardly deflecting positive polarity portion of thecurrently observed P wave) to the total deflection value of thecurrently observed P wave is calculated. The decision in decision block670 is “YES” when the negative/total deflection ratio is greater than orequal to a predetermined fraction (e.g., three quarters, seven eighths,etc.). Otherwise, the decision in decision block 670 is “NO.”

When the decision in decision block 670 is “YES,” the method 600advances to decision block 675. When the decision in decision block 670is “NO,” the method 600 returns to block 665.

In decision block 675, the current deflection ratio is compared to themaximum deflection ratio observed. The decision in decision block 675 is“YES” when the current deflection ratio is approximately equal to themaximum deflection ratio observed. By way of a non-limiting example, thecurrent deflection ratio may be considered approximately equal to themaximum deflection ratio observed when the absolute value of thedifference between the current deflection ratio and the maximumdeflection ratio observed is less than 0.2. If the current deflectionratio is not approximately equal to the maximum deflection ratioobserved, the decision in decision block 675 is “NO.”

When the decision in decision block 675 is “YES,” the method 600 ends.When the decision in decision block 675 is “NO,” the method 600 returnsto block 640.

When the decision in decision block 660 is “NO,” the current deflectionratio (calculated after the CVC 100 was advanced by the currentincremental distance) is greater than or equal to the previousdeflection ratio (calculated after the CVC 100 was advanced by theprevious incremental distance). When the decision in decision block 660is “NO,” the method 600 advances to decision block 680.

The decision in decision block 680 is “YES,” when the current deflectionratio is less than a maximum threshold value. Otherwise, decision indecision block 680 is “NO.” By way of a non-limiting example, themaximum threshold value may be about 8.0.

When the decision in decision block 680 is “YES,” the current deflectionratio is less than the maximum threshold value (e.g., 8.0) and greaterthan the previous deflection ratio. When this is the case, the method600 returns to block 640.

When the decision in decision block 680 is “NO,” the current deflectionratio is greater than or equal to the maximum threshold value (e.g.,8.0), and the method 600 advances to decision block 685 to determinewhether the current deflection ratio is approximately equal to themaximum threshold value.

When the current deflection ratio is approximately equal to the maximumthreshold value, the decision in decision block 685 is “YES.” Otherwise,decision in decision block 685 is “NO.” The current deflection ratio maybe considered approximately equal to the maximum threshold value whenthe absolute value of the difference between the current deflectionratio and the maximum threshold value is less than 0.2.

When the decision in decision block 685 is “YES,” the method 600 ends.When the decision in decision block 685 is “NO,” the current deflectionvalue is neither less than nor equal to the maximum threshold value.When this occurs, the method 600 progresses to block 686 whereat the CVC100 is withdrawn from the current location to a new location. Then, anew deflection value of the P wave observed at the new location ismeasured and a new deflection ratio of the new deflection value to thereference deflection value is calculated. The location of the CVC 100after withdrawal is a current location and the deflection ratiocalculated at the current location is a current deflection ratio. By wayof a non-limiting example, the CVC 100 may be withdrawn about 1 cm.Then, the method 600 advances to decision block 687.

In decision block 687, the current deflection ratio is compared to themaximum threshold value. The decision in decision block 670 is “YES”when the current deflection ratio is approximately equal to the maximumthreshold value. By way of a non-limiting example, the currentdeflection ratio may be considered approximately equal to the maximumthreshold value when the absolute value of the difference between thecurrent deflection ratio and the previous deflection ratio is less than0.2. When the current deflection ratio is not approximately equal to themaximum threshold value, the decision in decision block 687 is “NO.”

When the decision in decision block 687 is “YES,” the method 600 ends.When the decision in decision block 670 is “NO,” the method 600 advancesto decision block 690. Decision block 690 determines whether the CVC 100was withdrawn too far in block 686. The decision in decision block 690is “YES” when the current deflection ratio is less than maximumthreshold value. When this occurs, continuing to withdraw the CVC 100will simply reduce the current deflection value. Thus, to make thecurrent deflection ratio approximately equal to the maximum thresholdvalue, the CVC 100 must be advanced.

The decision in decision block 690 is “NO” when the current deflectionratio is greater than the maximum threshold value. Thus, to make thecurrent deflection ratio approximately equal to the maximum thresholdvalue, the CVC 100 must be withdrawn. When the decision in decisionblock 690 is “NO,” the method 600 returns to block 686.

If at anytime during the performance of the method 600, the currentdeflection ratio is approximately equal to the previously observedmaximum deflection ratio, advancement and withdrawal of the CVC 100 maybe halted and performance of the method 600 terminated. Similarly, if atanytime during the performance of the method 600, the current deflectionratio is approximately equal to the maximum threshold value, advancementand withdrawal of the CVC 100 is halted and performance of the method600 terminated.

Method of Using a Single Electrode Pair to Determine the Location of theTip of the Cvc within the Right Atrium

As discussed above, the P wave voltage is almost entirely negative atthe top of the right atrium (see trace 3 of FIG. 2B), biphasic in themid right atrium (see trace 4 of FIG. 2B), and positive at the bottom ofthe right atrium (see trace 5 of FIG. 2B). Referring to FIG. 6, a method190 uses these characteristics of the P wave voltage to determine thelocation of the tip 112 of the CVC 100 within the atrium. As is apparentto those of ordinary skill in the art, with respect to the method 190,either the unipolar “V” lead trace or the bipolar Lead II trace may beused.

In block 191, any method known in the art or described herein is used todetermine the tip 112 is located in the atrium. For example, the tip 112is in the atrium when the ratio of the deflection value of the currentlyobserved P wave to the reference deflection value is greater than avalue that may vary from person to person but is within a range of about4.0 to about 8.0. Alternatively, the tip 112 may be determined to be inthe atrium when the P wave voltage has exceeded a predetermined amount(e.g., about 0.8 mV to about 2.4 mV). Further, the tip 112 may bedetermined to be in the atrium when the positive/total deflection ratio(i.e., a ratio of the greatest positive deflection value of the initialupwardly deflecting portion of the currently observed P wave, whichprecedes a downwardly deflecting portion, to the total deflection value)is greater than the predetermined fraction (e.g., one quarter, oneeighth, etc.). By way of another example, the tip 112 may be determinedto be in the atrium when the voltage (or deflection value) of thecurrently observed P wave is approximately equivalent to or greater thanthe voltage (or deflection value) of the QRS complex.

After it is determined the tip 112 is in the right atrium, in block 192,a positive/negative deflection ratio is calculated. Thepositive/negative deflection ratio is a ratio of the greatest positivedeflection value to the smallest negative deflection value. As discussedabove, the absolute value of the deflection values may used. Thus, thepositive/negative deflection ratio may be calculated as a ratio of thedeflection value having the largest absolute value within the portion ofthe P wave that has a positive polarity to the deflection value havingthe largest absolute value within the portion of the P wave having anegative polarity. If the P wave is entirely negative, thepositive/negative ratio is zero (and the tip 112 is in the upperatrium). On the other hand, if the largest positive deflection value andthe smallest negative deflection value are equal, the positive/negativedeflection ratio is equal to one. In subsequent blocks 193-197, thepositive/negative deflection ratio is used to determine whether the tip112 is located in the upper, mid, or lower atrium.

In decision block 193, whether the positive/negative deflection ratio isless than a first predetermined threshold value is determined. The firstpredetermined threshold value may be about 0.80. If decision block 193determines the ratio is less than the first predetermined thresholdvalue, in block 194, the method 190 determines the tip 112 is in theupper atrium and the method 190 ends.

If decision block 193 determines the ratio is not less than the firstpredetermined threshold value, the method 190 advances to decision block195. In decision block 195, whether the positive/negative deflectionratio is greater than a second predetermined threshold value isdetermined. The second predetermined threshold value may be about 1.20.If decision block 195 determines the ratio is greater than the secondpredetermined threshold value, in block 196, the method 190 determinesthe tip 112 is in the lower atrium and the method 190 ends.

If decision block 195 determines the ratio is not greater than thesecond predetermined threshold value, in block 197, the method 190determines the tip 112 is in the mid atrium and the method 190 ends. Inother words, if the positive/negative deflection ratio is between thefirst and second predetermined threshold values, the tip 112 is in themid atrium. Further, if the positive/negative deflection ratio is equalto the first predetermined threshold value or the second predeterminedthreshold value, the tip 112 is in the mid atrium.

The following table summarizes the relationship between the location ofthe tip 112 of the CVC 100 and the positive/negative deflection ratio:

TABLE 2 Location of the tip 112 Upper Mid Lower Atrium Atrium AtriumPositive/Negative Deflection Ratio: <0.80 0.80-1.20 >1.20 ratio of thegreatest positive deflection value to the smallest negative deflectionvalue

While Table 2 provides exemplary ranges and/or threshold values for useas a general guideline, those of ordinary skill in the art appreciatethat these values may benefit from adjustment as additional anatomic orelectrophysiologic data is acquired and such modified values are withinthe scope of the present invention.

Embodiments Using Two or More Pairs of Electrodes

In the embodiment depicted in FIG. 3B, the CVC 100 includes fourlongitudinally spaced apart electrodes 150, 152, 154, and 156. Eachelectrode 150, 152, 154, and 156 is in electrical communication with awire 160, 162, 164, and 166, respectively. In particular embodiments,the electrodes 150, 152, 154, and 156 are constructed from the distalend of each of the wires 160, 162, 164, and 166. In another embodiment,the electrodes 150, 152, 154, and 156 are attached to the ends of thewires 160, 162, 164, and 166 by any method known in the art forattaching an electrode to a wire, including soldering. The wires 160,162, 164, and 166 are electrically isolated from one another. The wires160, 162, 164, and 166 may be insulated from the environment outside thebody 130 by the body 130.

The electrodes 150, 152, 154, and 156 and the wires 160, 162, 164, and166 may be constructed from any suitable materials known in the art suchas stainless steel or platinum. Alternatively, a column of conductivematerial such as an electrolytic material (e.g., saline) may be used toconstruct one or more of the electrodes 150, 152, 154, and 156 and/orthe wires 160, 162, 164, and 166. The electrodes 150, 152, 154, and 156may be about 6 mm to about 12 mm long, about 6 mm to about 12 mm wide,and about 1 mm to about 4 mm thick. The wires 160, 162, 164, and 166 maybe constructed using any electrical lead wire suitable for obtaining anECG trace.

Optionally, the invention may include two longitudinally spaced apartelectrodes 157 and 158. Each of the electrodes 157 and 158 may beelectrical communication with a wire 167 and 168, respectively. Theelectrodes 157 and 158 and wires 167 and 168 may be constructed in amanner substantially similar to that used to construct the electrodes150, 152, 154, and 156 and the wires 160, 162, 164, and 166,respectively. In particular embodiments, the electrode 157 and 158 arepositioned proximal to the electrodes 150, 152, 154, and 156.

Electrodes 150, 152, 154, and 156 may form two anode/cathode pairs. Forexample, electrodes 150 and 152 may form a first or proximalanode/cathode pair 180 and electrodes 154 and 156 may form a second ordistal anode/cathode pair 182. Optional electrodes 157 and 158 may forman optional third or reference anode/cathode pair 184. A pair ofelectrodes forming an anode/cathode pair may be attached to a pair ofinsulated wires housed within a single cable. In particular embodiments,a pair of bipolar lead wires are used. In this manner, the fourelectrodes of the proximal and distal anode/cathode pairs 180 and 182may be attached to two lead wires. A third bipolar lead wire may beincluded for use with the reference anode/cathode pair 184.Alternatively, the proximal and distal anode/cathode pairs 180 and 182may be attached to four insulated wires housed within a single cablesuch a dual bipolar lead wire.

The wires 160, 162, 164, and 166 and electrodes 150, 152, 154, and 156may be permanently embedded into the body 130 of the CVC 100 orremovably inserted into one or more channels or lumens 132 formed in theCVC 100 for potential future removal and/or replacement. The wires 167and 168 and electrodes 157 and 158 may be incorporated into the CVC 100in any manner described with respect to wires 160, 162, 164, and 166 andelectrodes 150, 152, 154, and 156, respectively.

The electrodes 150, 152, 154, and 156 are in electrical communicationwith the environment outside the CVC 100. In particular embodiments, aportion of each of the electrodes 150, 152, 154, and 156 are exposed tothe environment outside the CVC 100 by apertures 170, 172, 174, and 176formed in the body 130 adjacent to the electrodes 150, 152, 154, and156, respectively. In embodiments including optional electrodes 157 and158, a portion of each of the electrodes 157 and 158 may be exposed tothe environment outside the CVC 100 by apertures 177 and 178 formed inthe body 130 adjacent to the electrodes 157 and 158, respectively. Theapertures 177 and 178 may be constructed in any manner suitable forconstructing apertures 170, 172, 174, and 176. The apertures 170, 172,174, and 176 may be formed in the body 130 by any method known in theart and the invention is not limited by the method used to construct theapertures 170, 172, 174, and 176. While the electrodes 150, 152, 154,and 156 depicted in the drawings extend outwardly from the body 130through the apertures 170, 172, 174, and 176, it is understood by thoseof ordinary skill in the art, that electrodes 150, 152, 154, and 156 mayreside at the bottom of the apertures 170, 172, 174, and 176 which mayprovide a passageway for fluids in the outside environment to theelectrodes 150, 152, 154, and 156. Alternatively, the portion of theelectrodes 150, 152, 154, and 156 in electrical communication with theenvironment outside the CVC 100 may be flush with the outside surface ofthe CVC 100.

The electrode 156 may be located at or spaced from the tip 112. Inparticular embodiments, the electrode 156 is less than about 5 mm fromthe tip 112. The spacing between an anode and cathode of theanode/cathode pairs 180 and 182 may be about 1 mm to about 4 mm. Inparticular embodiments, the spacing between an anode and cathode of theanode/cathode pairs 180 and 182 is about 3 mm.

In particular embodiments, the distance between the electrodes 154 and152 is less than the height of the right atrium. In an adult, the heightof the right atrium may be approximately equal to or greater than about4 cm. In one exemplary embodiment, the distance between the electrode154 and 152 may be about 3 cm. In embodiments including optionalelectrodes 157 and 158, the distance between the electrodes 150 and 158may be about 10 cm to about 18 cm.

Those of ordinary skill in the art appreciate that the size and spacingof the electrodes provided herein may require modification for use withpatients that are larger or smaller than a typical adult and suchembodiments are within the scope of the present invention. For example,smaller electrodes with a closer spacing may be required for use with apediatric patient.

Referring to FIG. 7, the CVC 100 may gain venous access to the SVC byany method known in the art including inserting the CVC 100 in astandard sterile fashion through the subclavian, one of the jugularveins, or a peripheral vein and directing the tip 112 of the CVC 100through that vein to the SVC.

Each of the anode/cathode pairs 180 and 182 may be used to generate anECG trace. In this manner, the ECG waveforms detected by the proximalpair 180 may be compared to the ECG waveform detected by the distal pair182. In particular embodiments, the P wave portion of each trace iscompared to determine the position of the tip 112 of the CVC 100 withinthe SVC, right atrium, and right ventricle.

In embodiments including the reference anode/cathode pair 184, thereference anode/cathode pair 184 may be used to generate an ECG trace.Referring to FIG. 7, because the reference anode/cathode pairs 184 maybe located substantially proximally from the proximal and distalanode/cathode pairs 180 and 182, the reference anode/cathode pair 184may remain in the venous system proximal to or in the proximal SVC afterthe proximal and distal anode/cathode pairs 180 and 182 have entered theheart. In particular embodiments, the spacing between the anode/cathodepair 184 and the proximal pair 180 is large enough to insure thereference anode/cathode pair 184 remains proximal to or inside theproximal SVC when the distal anode/cathode pair 182 is inside the rightventricle. In this manner, the reference anode/cathode pair 184 may beused to detect the ECG waveform within venous system proximal to or inthe proximal SVC while the catheter is being placed.

The ECG waveforms detected by the proximal anode/cathode pair 180 and/ordistal anode/cathode pair 182 may be compared to the ECG waveformdetected by the reference anode/cathode pair 184. In particularembodiments, the P wave portion of the ECG trace detected by theproximal anode/cathode pair 180 and/or distal anode/cathode pair 182 iscompared to P wave portion of the ECG trace detected by the referenceanode/cathode pair 184 to determine whether the tip 112 of the CVC 100is located within the SVC, right atrium, or right ventricle.

Methods of Determining the Location of the Tip of the Cvc Using Two orMore Electrode Pairs

As is apparent to those of ordinary skill in the art, the methods 140,450, 190, and 600 described above may be performed using the CVC 100with two or three pairs of electrodes. With respect to each of themethods 140, 450, 190, and 600, the electrode 156 of the distalanode/cathode pair 182 may be substituted for the first electrode 114A(see FIG. 3A) and the electrode 154 of the distal anode/cathode pair 182may be substituted for the second electrode 114B (see FIG. 3A). By wayof another non-limiting example, any one of the electrodes 156, 154, or152 may be used as the cathode and any one of the electrodes 154, 152,or 150 proximal to the one used as the cathode may be used as the anode.Alternatively, with respect to each of the methods 140, 450, 190, and600, one or both of the distal anode/cathode pair 182 may be substitutedfor the first electrode 114A (see FIG. 3A) and one or both of theproximal anode/cathode pair 180 may be substituted for the secondelectrode 114B (see FIG. 3A). However, as is appreciated by those ofordinary skill in the art, it may be desirable to use the distal mostelectrode as the cathode.

Referring to FIG. 10, an alternate method 500 of determining thelocation of the tip 112 of the CVC 100 using two or three pairs ofelectrodes will now be described. With respect to method 500, unlessotherwise indicated, the deflection value is calculated as the sum ofthe absolute value of the maximum and minimum deflections when themaximum and minimum deflections have opposite polarities. The deflectionvalue is calculated as the larger of the absolute value of the maximumdeflection and the absolute value of the minimum deflection when themaximum and minimum deflections have the same polarity.

In first block 510, both the distal anode/cathode pair 182 and theproximal anode/cathode pair 180 are located in the venous systemproximal to or in the proximal SVC. A D/P ratio of the deflection valueof the distal anode/cathode pair 182 to the deflection value of theproximal anode/cathode pair 180 may be calculated and used to verify thelocations of the distal anode/cathode pair 182 and the proximalanode/cathode pair 180 within the venous system proximal to or in theproximal SVC. When both of the anode/cathode pairs 180 and 182 arewithin the venous system proximal to or in the proximal SVC, thedeflection value of the P wave detected by each of them is substantiallyidentical and the D/P ratio of their P wave deflection values equalsapproximately one. Optionally, the deflection value of one or both ofthe P waves may be stored or otherwise recorded. For example, thedeflection value of the P wave detected by the distal anode/cathode pair182 or the proximal anode/cathode pair 180 may be stored as a referencedeflection value.

In next block 518, the user advances the CVC 100. By way of anon-limiting example, the user may advance the CVC 100 about 0.5 cm toabout 1.0 cm. Then, in block 520, the D/P ratio of the deflection valueof the distal anode/cathode pair 182 to the deflection value of theproximal anode/cathode pair 180 is calculated. Optionally, thedeflection value of one or both of the P waves may be stored orotherwise recorded. Then, the method 500 advances to decision block 524.

The user or operator may wish to continue advancing the CVC 100 untilthe SA node is detected. When an anode/cathode pair 180 or 182 isapproximately 4 cm proximal to the SA node and therefore, by inference,approximately 4 cm proximal to the entrance of the right atrium (or“caval-atrial junction,” which is the location of the SA node), thedeflection value of the P wave detected by that anode/cathode pair mayincrease.

When the distal anode/cathode pair 182 enters the right atrium and theproximal anode/cathode pair 180 is still in the venous system proximalto or in the proximal SVC, the deflection value of the P wave detectedby the distal anode/cathode pair 182 may be at least four times thedeflection value of the P wave detected by the proximal anode/cathodepair 180. Therefore, when the D/P ratio of the P wave deflection valuesof the distal anode/cathode pair 182 to the proximal anode/cathode pair180 is greater than or equal to about 4.0 to about 8.0, the user oroperator should withdraw the CVC 100. By way of a non-limiting example,the user may withdraw the CVC 100 about 0.5 cm to about 1.0 cm.

In decision block 524, a predetermined maximum threshold value “TR1” maybe used to determine whether the user or operator should withdraw theCVC 100. If the D/P ratio exceeds the maximum threshold value “TR1,” thedecision in decision block 524 is “YES,” and in block 528, the CVC 100is withdrawn. In particular embodiments, the maximum threshold value“TR1” may range from approximately 4.0 to approximately 8.0. By way of anon-limiting example, the maximum threshold value “TR1” may be about8.0. If the D/P ratio does not exceed the maximum threshold value “TR1,”the decision in decision block 524 is “NO,” and the method 500 advancesto decision block 532.

When the distal anode/cathode pair 182 enters the right ventricle, theproximal anode/cathode pair 180 may be in the right atrium. Because thedeflection value of the P wave experienced in the right ventricle isapproximately equal to the deflection value of the P wave experienced inthe proximal SVC, the D/P ratio of the P wave deflection values of thedistal anode/cathode pair 182 to the proximal anode/cathode pair 180(which is now in the upper atrium) is less than or equal to about onehalf. Therefore, when the D/P ratio is less than about one half, theuser or operator should withdraw the CVC 100.

In decision block 532, a predetermined minimum threshold value “TMIN”may be used to determine whether the user or operator should withdrawthe CVC 100. If the D/P ratio is less than the predetermined minimumthreshold value “TMIN,” the decision in decision block 532 is “YES,” andin block 528, the CVC 100 is withdrawn. In particular embodiments, thepredetermined minimum threshold value “TMIN” may be approximately onehalf.

If the D/P ratio is not less than the minimum threshold value “TMIN,”the decision in decision block 532 is “NO,” and the distal anode/cathodepair 182 and the proximal anode/cathode pair 180 may both be in theright atrium at the same time. When this occurs, the deflection value ofthe P waves detected by each would be very similar if not identicalmaking their D/P ratio approximately equal to one. Therefore, in block536, a P/R ratio or D/R ratio (described below) may be calculated todetermine the location of the tip 112 of the CVC 100.

The P/R ratio may include the ratio of the deflection value of the Pwave detected by the proximal anode/cathode pair 180 to the storedreference deflection value of the P wave detected in the proximal SVC.In particular embodiments, the P/R ratio may include the ratio of thedeflection value of the P wave detected by the proximal anode/cathodepair 180 to a reference deflection value of the P wave detected by thereference anode/cathode pair 184. In embodiments that include areference anode/cathode pair 184, the reference anode/cathode pair 184may be used to detect the P wave in the proximal SVC. Because theproximal anode/cathode pair 180 is inside the right atrium, thedeflection value of its P wave is greater than or equal to about fourtimes to about eight times the deflection value of the P wave observedin the proximal SVC. When the P/R ratio is equal to or greater than athreshold value “TR2” within a range of about 4.0 to about 8.0, the useror operator should withdraw the CVC 100. By way of a non-limitingexample, the threshold value “TR2” may be about 4.0. By way of anon-limiting example, the threshold value “TR2” may be equal to thepredetermined maximum threshold value “TR1.” Alternatively, thethreshold value “TR2” could be set equal the largest D/R ratio observedthus far.

After the P/R ratio is calculated, in decision block 540, the thresholdvalue “TR2” may be used to determine whether the user or operator shouldwithdraw the CVC 100. If the P/R ratio exceeds the threshold value“TR2,” the decision in decision block 540 is “YES,” and in block 528,the CVC 100 is withdrawn. Otherwise, if the P/R ratio does not exceedthe threshold value “TR2,” the user does not need to withdraw the CVC100, and the decision in decision block 540 is “NO.” Then, the method500 ends.

Alternatively, in block 536, a D/R ratio may be calculated to determinethe location of the tip 112 of the CVC 100. The D/R ratio may includethe ratio of the deflection value of the P wave detected by the distalanode/cathode pair 182 to the stored reference deflection value of the Pwave detected in the proximal SVC. In particular embodiments, the D/Rratio may include the ratio of the deflection value of the P wavedetected by the distal anode/cathode pair 182 to the referencedeflection value of the P wave detected by the reference anode/cathodepair 184. In embodiments that include a reference pair 184, thereference pair 184 may be used to detect the P wave in the proximal SVC.Because the distal anode/cathode pair 182 is inside the right atrium,the deflection value of its P wave is greater than or equal to aboutfour times to about eight times the deflection value of the P waveobserved in the proximal SVC.

When D/R ratio is equal to or greater than a threshold value “TR3”within a range of about 4.0 to about 8.0, the user or operator shouldwithdraw the CVC 100. By way of a non-limiting example, the thresholdvalue “TR3” may be about 4.0. By way of a non-limiting example, thethreshold value “TR3” may be equal to the predetermined maximumthreshold value “TR1.” Alternatively, the threshold value “TR3” could beset equal the largest D/R ratio observed thus far. Under thesecircumstances, in decision block 540, the threshold value “TR3” may beused to determine whether the user or operator should withdraw the CVC100, i.e., if the D/R ratio exceeds the threshold value “TR3,” thedecision in decision block 540 is “YES,” and the CVC 100 is withdrawn inblock 528. Otherwise, if the D/R ratio does not exceed the thresholdvalue “TR3,” the user does not need to withdraw the CVC 100, and thedecision in decision block 540 is “NO.” Then, the method 500 ends.

After the CVC 100 is withdrawn in block 528, the method 500 may returnto block 520 to recalculate the D/P ratio.

In method 500, determining when to withdraw the CVC 100 is unaffected bywide anatomic variability between individual people because instead ofusing predetermined threshold deflection values, the D/P ratio, P/Rratio, and/or D/R ratio of deflection values obtained from eachindividual is used.

The following table summarizes the relationship between the location ofthe tip 112 of the CVC 100 and the deflection values of the P wavesdetected by the proximal and distal anode/cathode pairs 180 and 182:

TABLE 3 Location of the distal anode/cathode pair 182 Proximal RightRight Right SVC Atrium Atrium Ventricle Location of the proximalanode/cathode pair 180 Proximal Proximal Right Right SVC SVC AtriumAtrium D/P ratio: Ratio of the ≈1 ≧TR1 ≈1 ≦TMIN deflection value of thedistal anode/cathode pair 182 to the deflection value of the proximalanode/cathode pair 180 P/R ratio: Ratio of the ≈1 ≈1 ≧TR2 ≧TR2deflection value of the P wave detected by the proximal anode/cathodepair 180 and the deflection value of the P wave detected in the proximalSVC D/R ratio: Ratio of the ≈1 ≧TR3 ≧TR3 ≈1 deflection value of the Pwave detected by the distal anode/cathode pair 182 and the deflectionvalue of the P wave detected in the proximal SVC

As mentioned above, each of the threshold values “TR1,” “TR2,” and “TR3”in Table 3 may be within a range of about 4.0 to about 8.0 and theminimum threshold value “TMIN” may be about 0.5. Alternatively, thethreshold values “TR1,” “TR2,” and “TR3” in Table 3 may be set equal thelargest D/R ratio observed during the performance of the method 500. Byway of another example, the threshold values “TR1,” “TR2,” and “TR3” inTable 3 may be set equal the largest D/R ratio observed for the patientduring the performance of any of the methods described herein andrecorded for use with the method 500. While exemplary threshold values“TR1,” “TR2,” “TR3,” and “TMIN” have been provided for use as a generalguideline, those of ordinary skill in the art appreciate that thesevalues may benefit from adjustment as additional anatomic orelectrophysiologic data is acquired and such modified values are withinthe scope of the present invention.

As is apparent from Table 3, either of the P/R ratio and the D/R ratiomay be calculated first and used instead of the D/P ratio. For example,if the P/R ratio is calculated first, it may be compared to thethreshold value “TR2.” If the P/R ratio is greater than or equal to thethreshold value “TR2,” the tip 112 is in the right atrium or rightventricle and should be withdrawn. If the P/R ratio is less than thethreshold value “TR2,” the tip 112 is in the right atrium or proximalSVC. When this occurs, either the D/P ratio or the D/R ratio may becalculated. If the D/P ratio is calculated, it may be compared to thepredetermined maximum threshold value “TR1.” If the D/P ratio is greaterthan or equal to the predetermined maximum threshold value “TR1,” thetip 112 should be withdrawn. If the D/R ratio is calculated, it may becompared to the threshold value “TR3.” If the D/R ratio is greater thanor equal to the threshold value “TR3,” the tip 112 should be withdrawn.

Alternatively, if the D/R ratio is calculated first, it may be comparedto the threshold value “TR3.” If the D/R ratio is greater than or equalto the threshold value “TR3,” the tip 112 is in the right atrium andshould be withdrawn. If the D/R ratio is less than the threshold value“TR3,” the tip 112 is in the right ventricle or proximal SVC. When thisoccurs, either the D/P ratio or the P/R ratio may be calculated. If theD/P ratio is calculated, it may be compared to the predetermined minimumthreshold value “TMIN.” If the D/P ratio is less than or equal to thepredetermined minimum threshold value “TMIN,” the tip 112 should bewithdrawn. If the P/R ratio is calculated, it may be compared to thethreshold value “TR2.” If the P/R ratio is greater than or equal to thethreshold value “TR2,” the tip 112 should be withdrawn.

In addition to using the method 500 to determine when to withdraw theCVC 100, the QRS complex portion of the ECG waveforms detected by thedistal anode/cathode pair 182 and/or the proximal anode/cathode pair 180may be used to determine when the tip 112 of the CVC 100 is in the rightatrium. Specifically, the tip 112 should be withdrawn because it is inthe right atrium when the deflection value of the P wave detected byeither the distal anode/cathode pair 182 or the proximal anode/cathodepair 180 is approximately equivalent to or greater than the voltage (ordeflection value) of the QRS complex detected simultaneously by the sameanode/cathode pair. The P wave and QRS complex typically look similarand deflect in the same direction. The CVC 100 may be advanced until thedeflection value of the P wave is slightly less than or approximatelyequal to the deflection value of the QRS complex.

Further, a positive/total deflection ratio of the largest positivedeflection value (of an initial positive or upwardly deflecting portionpreceding a downwardly deflecting portion of a P wave detected by thedistal anode/cathode pair 182 and/or the proximal anode/cathode pair180) to the total deflection value (of the P wave detected by the distalanode/cathode pair 182 and/or the proximal anode/cathode pair 180) maybe used to determine when the tip 112 of the CVC 100 is in the rightatrium. As discussed above, the P wave voltage is almost entirelynegative at the top of the right atrium (see trace 3 of FIG. 2B),biphasic in the mid right atrium (see trace 4 of FIG. 2B), and positiveat the bottom of the right atrium (see trace 5 of FIG. 2B). Thus,advancement of the tip 112 may be halted when the positive/totaldeflection ratio is greater than a predetermined fraction (e.g., onequarter, one eighth, etc.). As mentioned above, with respect to thesingle electrode pair embodiments, when the positive/total deflectionratio exceeds the predetermined fraction, the tip 112 is in the rightatrium.

As is apparent to those of ordinary skill, the proximal and distalanode/cathode pairs 180 and 182 may be used to detect the instantaneouslocation of the tip 112. Therefore, if the tip 112 migrates into theatrium or ventricle, this movement may be detected immediately.Following such an occurrence, a medical professional may be alerted viaa signal, such as an alarm, and the like, to reposition the tip 112.

If the tip 112 is determined to be in the atrium, the method 190described above may be used to determine the position of the tip 112inside the atrium. Specifically, the electrode 114B (see FIG. 3A) may beattached to the skin of the patient. Then, the method 190 may be used todetermine a positive/negative deflection ratio for the P wave detectedby the electrode 114B and one of the electrodes 154 and 156 of thedistal anode/cathode pair 182. The positive/negative deflection ratiomay be compared to the first and second threshold values (see Table 2)and the location of the tip 112 within the atrium determined.Alternatively, instead of attaching the electrode 114B to the skin ofthe patient, one of the electrodes 157 and 158 of the referenceanode/cathode pair 184 may be used. In such embodiments, thepositive/negative deflection ratio is determined for the P wave detectedby one of the electrodes 157 and 158 of the reference anode/cathode pair184 and one of the electrodes 154 and 156 of the distal anode/cathodepair 182. As mentioned above, it may desirable to use the most distalelectrode 156 of the distal anode/cathode pair 182. Thepositive/negative deflection ratio may be compared to the first andsecond threshold values (see Table 2) and the location of the tip 112within the atrium determined.

Because the voltage across each of the anode/cathode pairs 180 and 182may vary depending over time, the voltage across wires 164 and 166 andwires 160 and 162 may each constitute a time-varying signal that can beanalyzed using standard signal processing methods well known in the art.In a typical patient, the maximum of voltage across the anode/cathodepairs 180 and 182 may range from about 0.2 mV to about 3 mV. The signalfrom each anode/cathode pairs 180 and 182 may be amplified and/orfiltered to improve the signal quality. A distal signal may be detectedby the distal anode/cathode pair 182 and a proximal signal may bedetected by the proximal anode/cathode pair 180. Similarly, an optionalreference signal may be detected by the reference anode/cathode pair184.

A separate ECG trace may be constructed for distal and proximal signals.In some embodiments, an ECG trace may also be constructed for thereference signal. The P wave portion of one or more of these ECG tracesmay be identified and analyzed. For example, the ECG trace of the distalsignal may be visualized by connecting wires 164 and 166 of the distalanode/cathode pair 182 to a device such as a PACERVIEW® signalconditioner designed specifically to construct and display an ECG tracefrom a time varying low voltage signal. Similarly, the ECG trace of theproximal signal may be viewed by connecting the wires 160 and 162 of theproximal anode/cathode pair 180 to a PACERVIEW® signal conditioner. TheECG trace of the reference signal may be viewed by connecting the wires167 and 168 of the proximal anode/cathode pair 184 to a PACERVIEW®signal conditioner.

In particular embodiments, each of the four wires 160, 162, 164, and 166may be coupled to a signal analysis system for analysis of the voltageinformation detected by the electrodes 150, 152, 154, and 156,respectively. In embodiments including electrodes 157 and 158, the wires167 and 168 may be coupled to the signal analysis system for analysis ofthe voltage information detected by the electrodes 157 and 158,respectively. An exemplary signal analysis system 200 for analyzing thesignals carried by wires 160, 162, 164, and 166 and alerting the user oroperator when to withdraw the tip 112 of the CVC 100 may be viewed inFIG. 7. In an alternate embodiment, the system 200 may also analyze thesignals carried by wires 167 and 168.

System 200

FIG. 8 is a block diagram of the components of the exemplary system 200.The system 200 may include a programmable central processing unit (CPU)210 which may be implemented by any known technology, such as amicroprocessor, microcontroller, application-specific integrated circuit(ASIC), digital signal processor (DSP), or the like. The CPU 200 may beintegrated into an electrical circuit, such as a conventional circuitboard, that supplies power to the CPU 210. The CPU 210 may includeinternal memory or memory 220 may be coupled thereto. The memory 220 maybe coupled to the CPU 210 by an internal bus 264.

The memory 220 may comprise random access memory (RAM) and read-onlymemory (ROM). The memory 220 contains instructions and data that controlthe operation of the CPU 210. The memory 220 may also include a basicinput/output system (BIOS), which contains the basic routines that helptransfer information between elements within the system 200. The presentinvention is not limited by the specific hardware component(s) used toimplement the CPU 210 or memory 220 components of the system 200.

All or a portion of the deflection values and/or deflection ratioscalculated by the methods 140, 190, 450, 500, and 600, including thereference deflection value, may be stored in the memory 220 for use bythe methods.

Optionally, the memory 220 may include external or removable memorydevices such as floppy disk drives and optical storage devices (e.g.,CD-ROM, R/W CD-ROM, DVD, and the like). The system 200 may also includeone or more I/O interfaces (not shown) such as a serial interface (e.g.,RS-232, RS-432, and the like), an IEEE-488 interface, a universal serialbus (USB) interface, a parallel interface, and the like, for thecommunication with removable memory devices such as flash memory drives,external floppy disk drives, and the like.

The system 200 may also include a user interface 240 such as a standardcomputer monitor, LCD, colored lights 242 (see FIG. 7), PACERVIEW®signal conditioner, ECG trace display device 244 (see FIG. 7), or othervisual display including a bedside display. In particular embodiments, amonitor or handheld LCD display may provide an image of a heart and avisual representation of the estimated location of the tip 112 of theCVC 100. The user interface 240 may also include an audio system capableof playing an audible signal. In particular embodiments, the userinterface 240 includes a red light indicating the CVC 100 should bewithdrawn and a green light indicating the CVC 100 may be advanced. Inanother embodiment, the user interface 240 includes an ECG trace displaydevice 244 capable of displaying the ECG trace of the distal andproximal signals. In the embodiment depicted in FIG. 7, the userinterface 240 includes a pair of lights 242, one red and the othergreen, connected in series with a ECG trace display device 244. In someembodiments, a display driver may provide an interface between the CPU210 and the user interface 240. Because an ultrasound machine istypically used when placing peripherally inserted central catheters(“PICC” lines), the system 200 may be incorporated into an ultrasoundunit (not shown).

The user interface 240 may permit the user to enter control commandsinto the system 200. For example, the user may command the system 200 tostore information such as the deflection value of the P wave inside theSVC. The user may also use the user interface 240 to identify whichportion of the ECG trace corresponds to the P wave. The user interface240 may also allow the user or operator to enter patient informationand/or annotate the data displayed by user interface 240 and/or storedin memory 220 by the CPU 210. The user interface 240 may include astandard keyboard, mouse, track ball, buttons, touch sensitive screen,wireless user input device and the like. The user interface 240 may becoupled to the CPU 210 by an internal bus 268.

Optionally, the system 200 may also include an antenna or other signalreceiving device (not shown) such as an optical sensor for receiving acommand signal such as a radio frequency (RF) or optical signal from awireless user interface device such as a remote control. The system 200may also include software components for interpreting the command signaland executing control commands included in the command signal. Thesesoftware components may be stored in memory 220.

The system 200 includes an input signal interface 250 for receiving thedistal and proximal signals. The input signal interface 250 may also beconfigured to receive the reference signal. The input signal interface250 may include any standard electrical interface known in the art forconnecting a double dipole lead wire to a conventional circuit board aswell as any components capable of communicating a low voltage timevarying signal from a pair of wires through an internal bus 262 to theCPU 210. The input signal interface 250 may include hardware componentssuch as memory as well as standard signal processing components such asan analog to digital converter, amplifiers, filters, and the like.

The various components of the system 200 may be coupled together by theinternal buses 262, 264, and 268. Each of the internal buses 262, 264,and 268 may be constructed using a data bus, control bus, power bus, I/Obus, and the like.

The system 200 may include instructions 300 executable by the CPU 210for processing and/or analyzing the distal and/or proximal signals.These instructions may include computer readable software components ormodules stored in the memory 220. In particular embodiments, theinstructions 300 include instructions for performing the method 500 (seeFIG. 10).

The instructions 300 may include an ECG Trace Generator Module 310 thatgenerates a traditional ECG trace from the distal and/or proximalsignals. In some embodiments, the ECG Trace Generator Module 310 maygenerate a traditional ECG trace from the reference signal. As isappreciated by those of ordinary skill in the art, generating an ECGtrace from an analog signal, such as the distal and proximal signals,may require digital or analog hardware components, such as an analog todigital converter, amplifiers, filters, and the like and suchembodiments are within the scope of the present invention. In particularembodiments, some or all of these components may be included in theinput signal interface 250. In an alternate embodiment, some or all ofthese components may be implemented by software instructions included inthe ECG Trace Generator Module 310. The ECG Trace Generator 310 mayinclude any method known in the art for generating an ECG trace from atime varying voltage signal.

The ECG Trace Generator 310 may record one or more of the ECG tracesgenerated. Presently, a chest x-ray is used to document the location ofthe tip 112. This documentation may be used to prove the tip 112 of theCVC was placed correctly. Using the present techniques, the recorded ECGtrace(s) may be used in addition to or instead of the chest x-ray todocument tip 112 location. For example, the recorded ECG trace(s) maydemonstrate that the tip 112 has migrated from the proximal SVC into theright atrium. Further, the recorded ECG trace(s) could document therepositioning of the tip 112 back into proximal SVC. Additionally, therecorded ECG trace(s) could document that the tip 112 was initiallyplaced correctly and did not migrate from its initial position. In thismanner, the ECG trace(s) could be used to document the correct orincorrect placement of the tip 112 and could be included in thepatient's medical record, replacing or supplementing the prior art chestx-ray. Further, if the tip 112 does migrate, the recorded ECG trace(s)could be used to determine whether the tip entered the atrium, how farinto the atrium the tip migrated, and/or whether the tip entered theventricle.

The instructions 300 may include a P Wave Detection Module 320 fordetecting or identifying the P wave portion of the ECG trace. The P waveportion of the ECG trace may be detected using any method known in theart. In particular embodiments, the P Wave Detection Module 320 receivesinput from the user or operator via the user interface 240. The inputreceived may identify the P wave portion of the ECG trace. Optionally,the P Wave Detection Module 320 may include instructions for identifyingthe QRS complex as well as the P wave portion of the ECG trace. Further,the P Wave Detection Module 320 may include instructions for determininga deflection value for an initial upwardly deflecting portion of asingle P wave preceding a downwardly deflecting portion. The P WaveDetection Module 320 may also include instructions for determining apositive/total deflection ratio of the largest positive deflection valuefor the initial upwardly deflecting portion of the P wave to thedeflection value for the entire P wave.

The instructions 300 may include an Interpretive Module 330 forcomparing the P wave generated for the distal, proximal, and/orreference signals. In particular embodiments, the Interpretive Module330 determines the deflection value of the P wave generated for thedistal and/or proximal signals. In some embodiments, the InterpretiveModule 330 determines the deflection value of the P wave generated forthe reference signal. The Interpretive Module 330 may direct the CPU 210to store the deflection value of the distal, proximal, and/or referencesignals in memory 220. In particular, it may be desirable to store thedeflection value of the P wave encountered in the proximal SVC. TheInterpretive Module 330 may receive input from the user or operator viathe user interface 240 instructing the Interpretive Module 330 to storethe deflection value. This information could be stored under a uniquepatient identifier such as a medical record number so that tip locationinformation could be accessed anytime during the life of the CVC 100,potentially avoiding the need for a chest x-ray to document currentlocation.

With respect to performing the method 500 illustrated in FIG. 10, theInterpretive Module 330 may also determine the D/P ratio by calculatingthe ratio of the deflection value of the distal signal to the deflectionvalue of the proximal signal. If the D/P ratio is approximately equal toor greater than the maximum threshold value “TR1,” the tip 112 of theCVC 100 may be in the right atrium. The Interpretive Module 330 mayalert the user or operator that the tip 112 is in the right atrium andthe CVC 100 should be withdrawn from the right atrium. On the otherhand, if the D/P ratio is approximately equal to or less than theminimum threshold value “TMIN,” the tip 112 of the CVC 100 may be in theright ventricle. The Interpretive Module 330 may alert the user oroperator that the tip 112 is in the right ventricle and the CVC 100should be withdrawn therefrom.

If the D/P ratio is less than the maximum threshold value “TR1” andgreater than the minimum threshold value “TMIN,” the tip 112 may be ineither the right atrium or the proximal SVC. When this happens, theInterpretive Module 330 may calculate the P/R ratio and/or the D/Rratio. For example, if the D/R ratio is approximately equal to orgreater than the threshold value “TR3,” the tip may be in the rightatrium and should be withdrawn therefrom. When this occurs, theInterpretive Module 330 may alert the user or operator that the tip 112is in the right atrium. If the D/R ratio is approximately less than thethreshold value“TR3,” the tip 112 is in the SVC and may be advanced ifthe operator so chooses. The Interpretive Module 330 may communicate tothe user or operator that the tip 112 may be advanced.

On the other hand, if the P/R ratio is approximately equal to or greaterthan the threshold value “TR2,” the tip may be in the right atrium orright ventricle and should be withdrawn therefrom. When this occurs, theInterpretive Module 330 may alert the user or operator to withdraw thetip 112. If the P/R ratio is approximately less than the thresholdvalue“TR2,” the tip 112 is in the SVC (because the D/P ratio is lessthan the maximum threshold value “TR1”) and may be advanced if theoperator so chooses. The Interpretive Module 330 may communicate to theuser or operator that the tip 112 may be advanced.

In an alternate embodiment, the P/R ratio is used instead of the D/Pratio. Whenever the P/R ratio is approximately equal to or greater thanthe threshold value “TR2,” the user or operator may be alerted towithdraw the CVC 100. If the P/R ratio is approximately less than thethreshold value “TR2,” the D/P ratio or D/R ratio may be calculated andused to determine the position of the tip 112 of the CVC 100.

In another alternate embodiment, the D/R ratio is used instead of theD/P ratio. Whenever the D/R ratio is approximately equal to or greaterthan the threshold value “TR3,” the user or operator may be alerted towithdraw the CVC 100. If the D/R ratio is approximately less than thethreshold value “TR3,” the D/R ratio or P/R ratio may be calculated andused to determine the position of the tip 112 of the CVC 100.

In particular embodiments, the instructions in the Interpretive Module330 direct the CPU 210 to use the user interface 240 to communicatewhether the tip 112 should be withdrawn to the user. The CPU 210 may usethe user interface 240 to communicate the tip 112 may be advanced.Because the Interpretive Module 330 may interpret the P wave to obtainthe deflection values of the distal and proximal signals, compare thedeflection values, and provide the operator with immediate real-timefeedback, the operator need not interpret the actual ECG waveforms.

Monitor 127

The monitor 127 of the system 121 for use with single pair of electrodeembodiments will now be described. Returning to FIG. 3A, forillustrative purposes, the monitor 127 is described as coupled to eachof the electrodes 114A and 114B by wires 123 and 129, respectively.However, in alternate embodiments, the monitor 127 is coupled to theelectrodes 176 and 174 of the distal anode/cathode pair 182 (see FIG.3B) by wires 123 and 129, respectively. By way of another alternateembodiment, one or both of the distal anode/cathode pair 182 may becoupled to the monitor 127 by wire 123 and one or both of the proximalanode/cathode pair 180 may be may be coupled to the monitor 127 by wire129.

Referring to FIG. 9, the monitor 127 includes a signal analysis system400 that may be substantially similar to the signal analysis system 200described above. Specifically, the system 400 may construct an ECG tracefor the electrical signals detected by the pair of electrodes 114, andidentify and analyze the P wave portion of the ECG trace using anymethod discussed above with respect to the system 200. Further, thesystem 400 is configured to display information to the user or operatorcommunicating the current position of the tip 112 of the CVC 100.

Like reference numerals are used to identify substantially identicalcomponents in FIGS. 8 and 9. The system 400 includes the CPU 210, thememory 220, the input signal interface 250 for receiving the signalsdetected by the pair of electrodes 114, and a user interface 410. Likesystem 200, the various components of the system 400 may be coupledtogether by the internal buses 262, 264, and 268.

All or a portion of the deflection values and/or deflection ratioscalculated by the methods 140, 190, 450, and 600, including thereference deflection value, may be stored in the memory 220 for use bythe methods.

The system 400 differs from the system 200 with respect to the userinterface 410 and at least a portion of the computer-executableinstructions stored in memory 220. Returning to FIG. 3A, in someembodiments, the user interface 410 includes an array of lights 412, afirst portion 412A of which corresponds to ratio values below or equalto the first predefined threshold value of the method 140 (see FIG. 4),a second portion 412B of which corresponds to the range of ratio valuesgreater than the first predefined threshold value and less than or equalto the second threshold value of the method 140, and a third portion412C of which indicates the second predefined threshold value has beenexceeded.

By way of a non-limiting example, the first portion 412A may include anarray of green lights. The number of green lights lit may indicate themagnitude of the ratio of the deflection value of the currently observedP wave to the reference deflection value. For example, the first portionmay include eight lights. The first light may indicate the ratio is lessthan or equal to 0.8. For each 0.2 increase in the ratio, another greenlight may be lit until all eight green lights are lit and the ratio isapproximately equal to 4.0. If the ratio decreases to less than 4.0, foreach 0.2 decrease in the ratio, a green light may be turned off untilonly a single green light is lit.

By way of a non-limiting example, the second portion of lights mayinclude an array of yellow lights. The number of yellow lights lit mayindicate the magnitude of the ratio of the deflection value of thecurrently observed P wave to the reference deflection value. Forexample, the second portion may include eight yellow lights. The firstyellow light may indicate the ratio is approximately equal to about 4.4to about 4.5. For each 0.2 increase in the ratio above 4.4, anotheryellow light may be lit until all eight yellow lights are lit and theratio is approximately equal to 6.0. If the ratio decreases to less than6.0, for each 0.2 decrease in the ratio, a yellow light may be turnedoff until the ratio is less than 4.4 and none of the yellow lights arelit.

By way of a non-limiting example, the third portion may include a singlered light indicating the magnitude of the ratio of the deflection valueof the currently observed P wave to the reference deflection value hasexceeded 6.0. If the ratio decreases to less than 6.0, the red light maybe turned off. In this manner, the user interface 410 provides greaterresolution for ratio values less than or equal to the first predefinedthreshold value than for ratio values between the first and secondpredefined threshold values.

While the above example has been described as including lights (such asLEDs, conventional light bulbs, and the like), those of ordinary skillin the art appreciate that any indicator may used and such embodimentsare within the scope of the present teachings. For example, a monitordisplaying a graphical representation of lights, a figure, such as abar, that increases or decreases in size to reflect an increase ordecrease in the ratio, and the like may be used in place of the array oflights. Optionally, the user interface 410 may include a screen 420 (seeFIG. 3A) configured to display information to the user or operator. Forexample, the screen 420 may display an image of a heart and a visualrepresentation of the estimated location of the tip 112 of the CVC 100.Alternatively, the screen 420 may display the words “ADVANCE,” “HOLD,”or “WITHDRAW” as appropriate.

The user interface 410 may also indicate when the tip 112 is located inthe ventricle. By way of a non-limiting example, the user interface 410may include a light, audio signal, or other indicator configured toindicate the tip 112 has entered the ventricle.

In some embodiments, a display driver may provide an interface betweenthe CPU 210 and the user interface 410. Optionally, the user interface410 includes an audio system capable of playing an audible signal. Forexample, the audio system may produce a tone that increases in pitch asthe ratio increases and decreases in pitch as the ratio decreases may beused. Alternatively, the audio system may produce one tone when theratio is greater than the first predefined threshold value, indicatingthe tip 112 should be withdrawn. In such embodiments, the audio systemmay produce another more urgent or annoying tone when the ratio is abovethe second predefined threshold value. Further, the audio system may besilent when the ratio is below the first predefined threshold value.

The user interface 410 may permit the user to enter control commandsinto the system 200. For example, the user may command the system 200 tostore information such as the deflection value of the P wave inside theproximal SVC (e.g., the reference deflection value), atrium (e.g., thereference atrium deflection value), and the like. The user may also usethe user interface 410 to identify manually which portion of the ECGtrace corresponds to the P wave. The user interface 410 may also allowthe user or operator to enter patient information (such as a patientidentifier number) and/or annotate the data displayed by user interface410 and/or stored in memory 220 by the CPU 210. The user interface 410may include a standard keyboard, mouse, track ball, buttons 416, touchsensitive screen, wireless user input device and the like. The userinterface 410 may be coupled to the CPU 210 by an internal bus 268.

By way of a non-limiting example, a patient's reference deflection value(detected when the tip 112 was located in the proximal SVC) and/orreference atrium deflection value (detected when the tip 112 was locatedin the atrium) could be stored in the memory 220 and associated with thepatient's patient identifier number or some other identification number.In this manner, the patient's recorded reference deflection value couldbe used anytime during the life of the CVC 100 by recalling thereference deflection value from memory 220 using the patient's patientidentifier number, which could be entered manually using the userinterface 410.

Optionally, the system 400 may also include an antenna or other signalreceiving device (not shown) such as an optical sensor for receiving acommand signal such as a radio frequency (RF) or optical signal from awireless user interface device such as a remote control. The system 400may also include software components for interpreting the command signaland executing control commands included in the command signal. Thesesoftware components may be stored in memory 220.

The system 400 includes instructions 300 executable by the CPU 210 forprocessing and/or analyzing the electrical signals detected by the pairof electrodes 114. The instructions 300 may include the ECG TraceGenerator Module 310 that generates a traditional ECG trace from thesignals detected by the pair of electrodes 114, the P Wave DetectionModule 320 for detecting or identifying the P wave portion of the ECGtrace, and the Interpretive Module 330. As discussed above with respectto the system 200, the ECG Trace Generator Module 310 may record the ECGtrace generated thereby.

Optionally, the P Wave Detection Module 320 may include instructions foridentifying the QRS complex as well as the P wave portion of the ECGtrace. Further, the P Wave Detection Module 320 may include instructionsfor determining a deflection value for an initial upwardly deflectingportion of a single P wave preceding a downwardly deflecting portion.The P Wave Detection Module 320 may also include instructions fordetermining a positive/total deflection ratio of the largest positivedeflection value for the initial upwardly deflecting portion of the Pwave to the deflection value for the entire P wave.

Like the Interpretive Module 330 of the system 200, the InterpretiveModule 330 of the system 400 determines the deflection value of the Pwave detected by a pair of electrodes (i.e., the pair of electrodes114). However, other functions performed by the Interpretive Module 330may differ in system 400 from those performed by the Interpretive Module330 in system 200. The Interpretive Module 330 directs the CPU 210 tostore the deflection value of the P wave detected by the pair ofelectrodes 114 in the proximal SVC in memory 220. The InterpretiveModule 330 may receive input from the user or operator via the userinterface 410 instructing the Interpretive Module 330 to store thedeflection value.

The Interpretive Module 330 also includes instructions for performingthe method 140, 190, and/or the method 600. With respect to the method140 (see FIG. 4), the Interpretive Module 330 may determine the ratio ofthe deflection value of the currently observed P wave to the referencedeflection value. The Interpretive Module 330 may compare this ratio tothe first predefined threshold (e.g., about 1.5). If the ratio is lessthan or equal to the first predefined threshold, the Interpretive Module330 determines the tip 112 is in the SVC. Further, if the determinationis made in block 143, the Interpretive Module 330 may signal the user oroperator to advance the tip 112. If the determination is made in block145, the Interpretive Module 330 may signal the user or operator to stopwithdrawing the tip 112.

If the ratio is greater than the first predefined threshold, theInterpretive Module 330 determines the tip 112 is not in a desiredlocation and instructs the user interface 410 to signal the user oroperator to withdraw the tip.

The Interpretive Module 330 may compare the ratio to the secondpredefined threshold value (e.g., about 2.0). If the ratio is less thanor equal to the second predefined threshold value, the InterpretiveModule 330 determines the tip 112 is in the distal SVC near the SA nodeor in the atrium near the SA node. If the ratio is greater than thesecond predefined threshold value, the Interpretive Module 330determines the tip 112 is in the atrium.

Optionally, the Interpretive Module 330 may determine the ratio of thedeflection value of the current P wave detected by the pair ofelectrodes 114 to the reference atrium deflection value. TheInterpretive Module 330 may compare this ratio to the third predefinedthreshold value (e.g., about 0.5) to determine whether the tip 112 is inthe atrium or the ventricle.

With respect to the method 190 (see FIG. 6), the Interpretive Module 330may determine the tip 112 is located within the right atrium using anymethod known in the art or disclosed herein. The Interpretive Module 330then calculates the positive/negative deflection ratio and compares thisratio to the first predetermined threshold value (e.g., about 0.30). Ifthe positive/negative deflection ratio is less than the firstpredetermined threshold value, the Interpretive Module 330 determinesthe tip 112 is in the upper right atrium. On the other hand, if thepositive/negative deflection ratio is greater than or equal to the firstpredetermined threshold value, the Interpretive Module 330 comparespositive/negative deflection ratio to the second predetermined thresholdvalue (e.g., about 1.30). If the positive/negative deflection ratio isgreater than the second predetermined threshold value, the InterpretiveModule 330 determines the tip 112 is in the lower atrium. Otherwise, ifthe positive/negative deflection ratio is greater than or equal to thefirst predetermined threshold value and less than or equal to the secondpredetermined threshold value, the Interpretive Module 330 determinesthe tip 112 is in the mid atrium.

With respect to the method 600 (see FIGS. 11A and 11B), the InterpretiveModule 330 may store a reference deflection value and determine thedeflection ratio of the deflection value of the currently observed Pwave to the reference deflection value. After the tip 112 is withdrawnor advanced, the Interpretive Module 330 may determine the currentdeflection ratio of the deflection value of the currently observed Pwave to the reference deflection value. The deflection ratio determinedbefore the tip 112 was withdrawn or advanced is stored by theInterpretive Module 330 as a previous deflection ratio.

Each time the tip 112 is moved (e.g., advanced or withdrawn), theInterpretive Module 330 determines whether the current deflection ratiois the largest observed since the CVC 100 was inserted into the venoussystem, and if the current deflection ratio is the largest deflectionratio observed, stores the current deflection ratio as the maximumdeflection ratio.

The Interpretive Module 330 compares the current deflection ratio to theprevious deflection ratio. If the current deflection ratio is less thanor equal to the previous deflection ratio, the Interpretive Module 330determines the tip 112 has been advanced too far and may signal the userto withdraw the CVC 100. Then, the Interpretive Module 330 determineswhether the tip 112 has been withdrawn far enough. The InterpretiveModule 330 may determine the tip 112 has been withdrawn far enough whenthe positive/total deflection ratio is less than a predeterminedfraction (e.g., one quarter, one eighth, etc.). Otherwise, the tip 112has not been withdrawn far enough. If the tip 112 has not been withdrawnfar enough, the Interpretive Module 330 signals the user to withdraw thetip 112.

If the tip 112 has been withdrawn far enough, the Interpretive Module330 determines whether the current deflection ratio is approximatelyequal to the maximum deflection ratio. If the current deflection ratiois not approximately equal to the maximum deflection ratio, theInterpretive Module 330 determines the tip 112 has been withdrawn toofar and signals the user to advance the CVC 100.

As mentioned above, the Interpretive Module 330 may compare currentdeflection ratio to the previous deflection ratio. If the currentdeflection ratio is greater than the previous deflection ratio, theInterpretive Module 330 determines whether the current deflection ratiois less than a maximum threshold value (e.g., 8.0). If the currentdeflection ratio is less than the maximum threshold value, theInterpretive Module 330 determines the tip 112 has not been advanced farenough and signals the user to advance the CVC 100.

If instead the current deflection ratio is greater than or equal to themaximum threshold value, the Interpretive Module 330 determines whetherthe current deflection ratio is approximately equal to the maximumthreshold value. If the current deflection ratio is not approximatelyequal to the maximum threshold value, the Interpretive Module 330determines the tip 112 has been advanced too far and signals the user towithdraw the CVC 100. After the tip 112 is withdrawn, the InterpretiveModule 330 determines whether the current deflection ratio isapproximately equal to the maximum threshold value.

If the current deflection ratio is not approximately equal to themaximum threshold value, the Interpretive Module 330 determines whetherthe current deflection ratio is less than the maximum threshold value(indicating the tip 112 has been withdrawn too far). If the currentdeflection ratio is less than the maximum threshold value, theInterpretive Module 330 determines the tip 112 has been withdrawn toofar and signals the user to advance the CVC 100. On the other hand, ifthe current deflection ratio is still greater than the maximum thresholdvalue, the Interpretive Module 330 determines the tip 112 has not beenwithdrawn far enough and signals the user to withdraw the CVC 100.

Optionally, whenever the current deflection ratio is approximately equalto the maximum deflection ratio or the maximum threshold value, theInterpretive Module 330 may signal the user to stop moving (e.g.,advancing or withdrawing) the CVC 100.

With respect to the methods 140, 190, and 600, the instructions in theInterpretive Module 330 direct the CPU 210 to use the user interface 410to communicate whether the tip 112 should be withdrawn to the user.Further, the instructions in the Interpretive Module 330 direct the CPU210 to use the user interface 410 to communicate the tip 112 may beadvanced. Because the Interpretive Module 330 may interpret the P waveto obtain the deflection values, compare the deflection values, andprovide the operator with immediate real-time feedback, the operatorneed not interpret the actual ECG waveforms.

Optionally, the system 400 could be coupled to a prior art navigationalsystem, such as a VIASYS MedSystems NAVIGATØR® BioNavigation® system,manufactured by VIASYS Healthcare Inc. of Conshohocken, Pa., which isprincipally used to guide peripherally placed lines, such as aperipherally inserted central catheter (“PICC”). Such systems determinethe location of a PICC line using magnetic fields that are generated bya detector, and detected by a magnetically activated position sensorlocated in the tip of a stylet inserted inside the PICC near its tip. Byway of a non-limiting example, the detector may include a NAVIGATØR®electronic locating instrument configured to emit low-level,high-frequency magnetic fields. Also by way of a non-limiting example,the stylet may include a MAPCath® Sensor Stylet also manufactured byVIASYS Healthcare Inc.

The sensor in the tip of the stylet is activated by the magnetic fieldemitted by the detector. The sensor is operable to output its locationvia a wire coupled to the sensor and extending longitudinally along thePICC to the detector, which is configured to interpret the signal andcommunicate the location of the tip to the user or operator. Asmentioned above, because such navigational systems depend upon arelationship between surface landmarks and anatomic locations, theycannot be used to determine the location of the tip 112 of the CVC 100with sufficient accuracy. However, the system 400 may be used, inconjunction with a navigational system to improve the accuracy of thenavigational system.

By way of non-limiting examples, additional prior art navigationalsystems include the Sherlock Tip Location System used with the styletprovided in Bard Access Systems PICC kits both of which are manufacturedby C. R. Bard, Inc. of Salt Lake City, Utah, the CathRite™ systemmanufactured by Micronix Pty. Ltd. of Australia, and the like. As isapparent to those of ordinary skill in the art, the present teaching maybe combined with one or more of these additional exemplary navigationalsystems and used to improve the accuracy of those systems.

In further embodiments, the teachings provided herein may be expanded touse electrophysiology procedures for navigating other bodily channels.For example, in the prior art, ECG guidance techniques have been used toplace feeding tubes. Because the QRS complex measured in the stomach isupright but in a post pyloric area (first part of the duodenum, beyondthe stomach) the QRS complex is down-going, one or more thresholddeflection values may be determined and used to determine the placementof the tip of the feeding tube.

The foregoing described embodiments depict different componentscontained within, or connected with, different other components. It isto be understood that such depicted architectures are merely exemplary,and that in fact many other architectures can be implemented whichachieve the same functionality. In a conceptual sense, any arrangementof components to achieve the same functionality is effectively“associated” such that the desired functionality is achieved. Hence, anytwo components herein combined to achieve a particular functionality canbe seen as “associated with” each other such that the desiredfunctionality is achieved, irrespective of architectures or intermedialcomponents. Likewise, any two components so associated can also beviewed as being “operably connected”, or “operably coupled”, to eachother to achieve the desired functionality.

While particular embodiments of the present invention have been shownand described, it will be obvious to those skilled in the art that,based upon the teachings herein, changes and modifications may be madewithout departing from this invention and its broader aspects and,therefore, the appended claims are to encompass within their scope allsuch changes and modifications as are within the true spirit and scopeof this invention. Furthermore, it is to be understood that theinvention is solely defined by the appended claims. It will beunderstood by those within the art that, in general, terms used herein,and especially in the appended claims (e.g., bodies of the appendedclaims) are generally intended as “open” terms (e.g., the term“including” should be interpreted as “including but not limited to,” theterm “having” should be interpreted as “having at least,” the term“includes” should be interpreted as “includes but is not limited to,”etc.). It will be further understood by those within the art that if aspecific number of an introduced claim recitation is intended, such anintent will be explicitly recited in the claim, and in the absence ofsuch recitation no such intent is present. For example, as an aid tounderstanding, the following appended claims may contain usage of theintroductory phrases “at least one” and “one or more” to introduce claimrecitations. However, the use of such phrases should not be construed toimply that the introduction of a claim recitation by the indefinitearticles “a” or “an” limits any particular claim containing suchintroduced claim recitation to inventions containing only one suchrecitation, even when the same claim includes the introductory phrases“one or more” or “at least one” and indefinite articles such as “a” or“an” (e.g., “a” and/or “an” should typically be interpreted to mean “atleast one” or “one or more”); the same holds true for the use ofdefinite articles used to introduce claim recitations. In addition, evenif a specific number of an introduced claim recitation is explicitlyrecited, those skilled in the art will recognize that such recitationshould typically be interpreted to mean at least the recited number(e.g., the bare recitation of “two recitations,” without othermodifiers, typically means at least two recitations, or two or morerecitations).

Accordingly, the invention is not limited except as by the appendedclaims.

The invention claimed is:
 1. A method of determining in which portion ofthe atrium a tip of a central venous catheter is located, the methodcomprising: obtaining an electrical signal from a portion of the atriumadjacent the tip of the central venous catheter; generating a P wavefrom the electrical signal; determining a greatest positive deflectionvalue for the reference P wave; determining a smallest negativedeflection value for the reference P wave; calculating a ratio of thegreatest positive deflection value to the smallest negative deflectionvalue; comparing the ratio to a first threshold value; if the ratio isless than the first threshold value, determining the tip is in the upperatrium; comparing the ratio to a second threshold value; if the ratio isgreater than the second threshold value, determining the tip is in thelower atrium; and if the ratio is greater than or equal to the firstthreshold value, and the ratio is less than or equal to the secondthreshold value, determining the tip is in the mid atrium.
 2. Acomputer-readable medium storing computer executable instructions fordirecting a processor to: obtain a reference deflection value from areference electrical signal detected near a tip of a central venouscatheter when the tip was located in a first position inside thesuperior vena cava; obtain a new deflection value from a new electricalsignal detected near the tip of a central venous catheter after the tipwas relocated from the first position to a second position; calculate aratio of the new deflection value to the reference deflection value;compare the ratio to a threshold value; if the ratio is less than thethreshold value, signal to a user the tip may be advanced; and if theratio is greater than the threshold value, signal to the user towithdraw the tip.
 3. A method of determining a location of a tip of acentral venous catheter having an electrode disposed inside the venoussystem of a subject, the venous system of the subject comprising asuperior vena cava having a proximal portion near a sino-atrial node,the method comprising: positioning the tip of the central venouscatheter within the venous system of the subject proximal to or within aproximal portion of the superior vena cava; while the tip is positionedproximal to or within a proximal portion of the superior vena cava,generating a reference P wave using the electrode; determining areference deflection value of the reference P wave; one of advancing andwithdrawing the tip of the central venous catheter to a first position;while the tip is in the first position, generating a first P wave usingthe electrode; determining a first deflection value of the first P wave;calculating a first ratio of the first deflection value to the referencedeflection value; one of advancing and withdrawing the tip of thecentral venous catheter to a second position; while the tip is in thesecond position, generating a second P wave using the electrode;determining a second deflection value of the second P wave; calculatinga second ratio of the second deflection value to the referencedeflection value; comparing the first ratio to the second ratio; if thesecond ratio is less than the first ratio, withdrawing the tip of thecentral venous catheter until a P wave generated using the electrode hasa minimum negative deflection value that is greater than a predeterminedportion of the second deflection value of the second P wave; and if thesecond ratio is greater than the first ratio, determining whether thesecond ratio exceeds a maximum threshold value, if the second ratio doesnot exceed the maximum threshold value, advancing the tip of the centralvenous catheter and if the second ratio exceeds the maximum thresholdvalue, withdrawing the tip of the central venous catheter.
 4. The methodof claim 3, further comprising: after each time the tip of the centralvenous catheter is advanced or withdrawn, generating a new P wave usingthe electrode, determining a new deflection value of the new P wave, anddetermining a new ratio of the new deflection value to the referencedeflection value; identifying a maximum ratio using the new ratiodetermined after each time the tip of the central venous catheter isadvanced or withdrawn; if the second ratio is less than the first ratio,after the tip of the central venous catheter has been withdrawn untilthe minimum negative deflection value is greater than the predeterminedportion of the second deflection value of the second P wave, the tip islocated in a current location, generating a current P wave using theelectrode, determining a current deflection value of the current P wave,and determining a current ratio of the current deflection value to thereference deflection value; and determining whether the current ratio isapproximately equal to the maximum ratio and if the current ratio isapproximately equal to the maximum ratio, maintaining the tip of thecentral venous catheter in its present location.
 5. The method of claim4, further comprising if the current ratio is not approximately equal tothe maximum ratio, advancing the tip of the central venous catheter. 6.The method of claim 4, wherein the predetermined portion of the P waveis greater than three quarters of the total P wave.
 7. The method ofclaim 3, wherein the predetermined portion of the P wave is greater thanseven eighths of the total P wave.
 8. The method of claim 3, furthercomprising if the second ratio is approximately equal to the maximumthreshold value, maintaining the tip of the central venous catheter inits present location.
 9. The method of claim 3, further comprising:after each time the tip of the central venous catheter is advanced orwithdrawn, generating a new P wave using the electrode, determining anew deflection value of the new P wave, and determining a new ratio ofthe new deflection value to the reference deflection value; identifyinga maximum ratio using the new ratio determined after each time the tipof the central venous catheter is advanced or withdrawn; one ofadvancing and withdrawing the tip to a current location; generating acurrent P wave using the electrode; determining a current deflectionvalue of the current P wave; determining a current ratio of the currentdeflection value to the reference deflection value; and determiningwhether the current ratio is approximately equal to the maximum ratioand if the current ratio is approximately equal to the maximum ratio,maintaining the tip of the central venous catheter in its presentlocation.
 10. A method of determining a location of a tip of a centralvenous catheter having an electrode disposed inside the venous system ofa subject, the venous system of the subject comprising a superior venacava having a proximal portion near a sino-atrial node, the methodcomprising: at least one of advancing and withdrawing the tip thecentral venous catheter; after each advancement or withdrawal of the tipof the central venous catheter, generating a new P wave using theelectrode, determining a new deflection value of the new P wave, anddetermining a new ratio of the new deflection value to the referencedeflection value; identifying a maximum ratio using the new ratiodetermined after each advancement or withdrawal of the tip of thecentral venous catheter; one of advancing and withdrawing the tip to acurrent location; generating a current P wave using the electrode;determining a current deflection value of the current P wave;determining a current ratio of the current deflection value to thereference deflection value; determining whether the current P wave has aminimum negative deflection value that is greater than a predeterminedportion of the current P wave; and determining whether the current ratiois approximately equal to the maximum ratio and if the current ratio isapproximately equal to the maximum ratio, maintaining the tip of thecentral venous catheter in its present location.
 11. The method of claim10, further comprising determining whether the current ratio exceeds amaximum threshold value, if the current ratio does not exceed themaximum threshold value, advancing the tip of the central venouscatheter and if the current ratio exceeds the maximum threshold value,withdrawing the tip of the central venous catheter.
 12. A monitorelectrically couplable to an electrode attached to a tip of a centralvenous catheter that is insertable into a venous system of a subject,the monitor comprising: a processor; a withdraw indicator coupled to theprocessor configured to indicate when the tip of the central venouscatheter should be withdrawn; and a memory coupled to the processor andhaving instructions executable by the processor, when executed, theinstructions instructing the processor to: store an identifieridentifying the subject, determine and store a reference deflectionvalue of a P wave detected by the electrode attached to the tip of thecentral venous catheter, associate the reference deflection value withthe identifier identifying the subject, determine a current deflectionvalue of a current P wave detected by the electrode attached to the tipof the central venous catheter, calculate a current ratio of the currentdeflection value to the stored reference deflection value, and actuatethe withdraw indicator to indicate the tip of the central venouscatheter should be withdrawn based on the current ratio.
 13. The monitorof claim 12, wherein the instructions executable by the processorfurther instruct the processor to: store a maximum ratio comprising alargest ratio of the current deflection value to the stored referencedeflection value calculated for the subject, associate the maximum ratiowith the identifier identifying the subject, compare the current ratioto the maximum ratio, and actuate the withdraw indicator to indicate thetip of the central venous catheter should be withdrawn based on thecomparison.
 14. The monitor of claim 12, wherein the instructionsexecutable by the processor further instruct the processor to comparethe current ratio to a threshold value and actuate the withdrawindicator to indicate the tip of the central venous catheter should bewithdrawn based on the comparison.
 15. The monitor of claim 12, whereinthe instructions executable by the processor further instruct theprocessor to store at least one of the current deflection value and thecurrent ratio.